At 50 yards, my .30 Impact is stacking in the same hole at 900 FPS even. It seems to be real happy from 880ish up to about 905 or 910 then it starts to open up into a cloverleaf. I have not tried going up into the mid 900s with pellets in it.
I seriously doubt that the .35 Impact is lacking in power, at least the current spec MK ll version. My .30 is current spec with Power Plenum, bigger valve seat, short preload adjuster etc. , and it is sitting at 105 bar with a whole bunch of hammer preload left. Considering that the air pressure is going to exert more energy on a .35 pellet than a .30, I think that the .35 would make some pretty respectable numbers.