I'm sure others with more experience will chime in here. But for me - the DF700 is a compliment to the DF500. Not an upgrade.

I haven't upgraded to the DF700, but have used both machines (and I disagree that the DF700 is as easy to handle as the DF500 which is lighter given my physical size and age, and the large number of mortises I mill on average). The thickness of the work isn't an issue; both can handle 3/4" well. It's the desired depths of the mortises that matter.

For big projects that require deep mortises, heavy doors or big tables, for example, you'll need the DF700. If your plan is to keep on working with 3/4" stock, the switch to a larger joiner won't bring you any added benefits -- unless you aren't happy with the DF500 in certain aspects.

I agree it’s too expensive, but if a project or a remodel justifies the cost then it’s worth the outlay of $NAP (North American Pesos). A lightly used 1-2 year old D700 would probably fetch $1,000 or more. It’s one of the tools that’s on the Festool Bucket List. 🪣

I just got my d500 not too long ago, so it will be in (mid) year 2021 that I get a D700
As others have said they compliment each other.

I agree that they compliment each other, but for a percentage of users, only one might be needed.
I see them as DF500 for sheet goods and cabinets, and the DF700 for larger solid wood projects like doors and table/apron joints.
If you do both, you need both, otherwise stick with the one in for your needs.
I have had a DF500 for 6 years and would like to have a DF700, but I have really only "needed it" 2 or 3 times in that amount of time. I worked-around it with a few more of the smaller tenons, but it wasn't ideal.
As I have said several times, I work in a big cabinet shop, so I don't get to choose what I build, as a hobbyist would. In general, I have to be equipped for nearly any unknown project and big solid wood things just don't happen that often.....still want one though.

I think for most the D500 is a better machine for starters since it’s less money. The D700 with the Seneca is a nice option, but I felt the heft of the tool was better for dimensional lumber, furniture, doors, gates, outdoor decks, tables, etc. @Blues What was your opinion of the Lamello zeta? I think there process is very nice and it would be a toss up between the DD40 and the Zeta for me?

I think for most the D500 is a better machine for starters since it’s less money. The D700 with the Seneca is a nice option, but I felt the heft of the tool was better for dimensional lumber, furniture, doors, gates, outdoor decks, tables, etc. @Blues What was your opinion of the Lamello zeta? I think there process is very nice and it would be a toss up between the DD40 and the Zeta for me?

The Lamello Zeta P2 is a fabulous tool too. I use it in many situations along with the DF500. They work great in situations were clamping is difficult. Large assemblies, wall panels etc.  I use the Clamex and the Tenso, depending on the situation. Dominos are great for alignment, but they won't pull an assembly together like they can.
I'm in a bit of a unique case though. Many of the things I build have to be disassembled for shipping to a jobsite. Then they get reassembled by someone else. It is rare that I go out to do the install, but I try to make them as easy to put back together as possible.

The obvious answer to this endless debate on 500 vs 700 is to buy both. That’s what my Festool dealer told me.

Hahaha. It always feels good when we can convince someone to spend their money away. Getting both should work for most Festool fans where budget is not a hurdle. But I must say I'm one of the exceptions while I can afford to have both as a hobbyist.

The only reason I'm not having two DFs is that I hate to see a good tool sitting idle in my shop. May be 5% of my furniture builds, if not less, could justify the use of an XL, but I feared that soon I'd resell it. (For the record, I made a small profit when I sold my TS75 and CT26.)

This tool philosophy of mine is why I keep looking around in my shop, trying to find and sell dormant or surplus tools that see little use -- especially when I get a new tool that duplicates some of the functions of an existing one.

Cases in point: Once I got skilled in the DF500, I immediately sold my Delta benchtop mortiser and biscuit joiner. My Dewalt miter saw was gone as soon as the Kapex was set up and tuned. And after building a planing jig for use with my thickness planer, I sold my jointer, too.

I also find that if I have just enough tools, I tend to develop expertise in each one of them because of constant use, while finding new uses of them, too. I'm pretty sure if I had had a DF700 around when I built my nook table, I wouldn't have bothered to learn about twin tenons and how they could help in my projects.

I was kind of on the opposite end of this situation, having the XL700 and then getting the DF500 although it's not as simple as that. I originally bought both machines a number of years back but went on to sell the DF as I figured the XL was suffice for my needs. I regretted selling the DF as soon as it went out the door and recently repurchased a new DF.

As others have pointed out above, I found I reached for the DF more than the XL even if they were both a relevant fit to the job. The XL feels like a better machine but when you're cutting a lot of mortises then the DF is probably easier on your arms. I also wouldn't consider the XL an upgrade to the DF either, it is suitable for different jobs and different ways of working. If you don't build larger items then the DF is perfect, but if you do a mix of mortising sheet / cabinetry and large project then both probably makes sense. You can get a Domiplate for the XL which will handle sheet but then you ned the RTS adapter and you could argue that that eats into the budget of owning both machines as opposed to one.

Long story short - if the DF does what you want, there is no merit in 'upgrading' to the XL. If you want the convenience of the DF but feel you would benefit from the additional capacity of the XL then buy an XL as well, not instead.

I have both a trim hammer and a framing hammer.  I tend to use my trim hammer the most.......

Great analogy...so easy to understand. 

had the 500 but needed to add the 700 for making a bed. Can't be bad to have both!