Lee, a 2.05 screen will show more of the IMAX scenes in TDK than a 2.35 screen will. You would need a standard 1.78 screen the width of what you want 2.35 films to be, to have TDK projected without cropping though.
The largest you can go is a 115" wide 2.35 image from 13ft throw. This would give you a 85" wide 16x9 image (98" diagonal).
If you want a 90" diagonal 16x9 image on a 2.35 screen, you'd need a 104" wide 2.35 image. This is probably more reasonable, since you won't find a pulldown that will fit 10ft and have a 115" wide viewable image I'm thinking.
If you want to use a 2.05 screen, you can do 104" wide (8.67 ft) like above, but your 16x9 image will now be 90" wide (103" diagonal), and feel the same size as 2.35 material (in a different shape).
You can also do constant area with the same dimensions (104" wide 2.35, and 90" wide 1.78) but with a 1.78 screen (same width, just taller) to allow you to open the masks and show TDK full screen width and height. This would require a ~120" diagonal 16x9 screen.
1.78 pulldowns are easy to come across. It's hard enough finding 2.35 pulldowns in a decent price range, much less 2.05, but I'm sure someone like Da-Lite would custom build any ratio you want.
Masking will be an issue with a pulldown though, and if you want less masking hassle you'll want either a 2.35 or 2.05 screen.
Even better would be to buy two pulldowns, one 16x9 the size you want, and one 2.35 the size you want, and just switch between the two. This way masking wouldn't be needed. TDK would have to be shown on the 16x9 screen, unless you had a VP that did cropping.
Here's a good example of a dual-screen CIA setup that also happens to use the 3000U, due to the Memory Lens that makes this so easy: http://www.avsforum.com/avs-vb/showthread.php?t=1108874