I have (and frequently use) both, going as far as having 2 OF1010, so my main consideration would be in how you are going to use it. First off, the 8mm shanks are not a deal-breaker. They are out there, just not "on the shelf" at your local home center.
You mention coves and rabbets, which are edge profiles. The chip collection capability of Festool routers shines here. The real question is "how often are you going to swap attachments?" The beauty of the OF1400 is the snap-in style mechanism of the base plate. The chip deflector, opening reducer, table-widener, and copy-rings (bushings) all snap in and out instantly and toolless. It is a bigger/heavier machine though, so if you don't need the greater power on these simple edge cuts, you don't need to deal with the weight either.
This is where the OF1010 comes in. It can do your edge/profile cuts easily too, in a much lighter more compact unit. The down-side of it is those same base-plate attachments. They exist, essentially the same, but they are more "fiddley". They are held on by 2 screws, which takes more time/effort...and a tool (2 actually) The copy-rings (bushings) are arguably better, because the are "center-able". (Which is a complete topic itself) But, they take different screws than the other parts which fit into the base, chip deflector, etc.
I have never experienced a lack of power with the OF1010, but I don't use it for everything.
If you "need" a plunge router specifically, the OF1010 is probably the best choice. Plunging cuts are generally, smaller bits in the first place. You don't "need" a plunge router for big things like panel raising. That would be better done on your router table anyway. The only reason I can see to pick the OF1400, in this specific case, is if the instant snap-in base pieces appeal to you.