I had several large tabletops machined that had 3/4" holes on a 4" grid.  I used the Festool clamps, then switched to the less expensive Powertec ones (that are identical to the ones on Woodpecker's site, but $5 less per pair).  All of those clamps have a little more than 2" throat depth.  I kept some 1" spacer blocks on hand that could offset the work from the dogs for clamping.  At no time using this system did I ever wish there were t-slots in it, as the holes/clamp combination allowed me to easily reach just about everything.  For weird stuff, I could make weird cauls or use bolts and straps.