You are correct. I checked www.tirerack.com
. The load ratings are all enough to meet or exceed what the axles can handle, and the gear ratio increases range from 10% to 14%. The 305 size however will NOT work because it requires a minimum 10.5 inch rim width, per the tire manufacturers' specs. The other sizes are good though.
I need to get a photoshop mockup for appearance. That's going to be, as Rick418cars suggests above, the determinging factor.
I HAVE been able to start modeling in the software tonight. The SSR IS indeed very responsive to gearing changes, because of its high weight. Upping the gearing by 10% reduces 0 to 60 time by 0.36 second. Upping the gearing by 14% reduces 0 to 60 by slightly over half a second!
The 14% is achieved via the 295/25 -20 tire size (which as you point out IS available). But, the drop in height is 1 3/4 inches(!!) and the appearance is a key question. hence, the need for a Photoshop mockup.