Here are replies I received from the software makers. If anyone else has any info, let me know.

Cardonware
We currently support the Axim x50s and don't have much experience with
the other HP models at this time. The x50v IrDA is top mounted and has
very good range even without our UltraMote Extender(r). The x50v is a
super PDA and is great for home multitasking as described in our recent
article on Hometoys. We can also add you to our notification list and
email you if we add either the 47xx or 27xx in future versions.

WinCeSoft
Haven't tested the iPAQ 4705 and 2750, but have some customers which have
bought RC II for these models.
I can attest the Dell x50v a good CIR- transmit range because I'm using it.
One of next versions of RC II will have a screen rotate function, so the IR
transceiver at the bottom of the hx4700 should be no problem.

Griffin Technologies
We have not tested the PDAs you have listed, so we can not make any
comment on their functionality with the Total Remote Software. We have
stopped development on the software so there will likely be no future
updates.