[gearheadgreg]

I haven't used or built any shaftless style throttle bodies, but I've been around them and talked with people that have built and used them - so for what that's worth: The slide throttle setup seems to be hard to make easily progressive at lighter openings, because the vacuum is pulling the slide against it's runner/guide etc. Barrel throttles don't seem to have that issue, but more of a seal/leak issue due to the machining involved.

These shaftless ones - I'd be interested to hear about as well. From old flowbench work, of course reducing or removing the shaft increases max flow, but if the throttle bodies flow more air than the engine can use at redline, it's no benefit...