Modded using the stock motors and a 9.6v NiMH battery, so thought I'd get a more middling crush level to keep from overwhelming the motors; I settled on the 42mm cage, and I regret it. It seems to shoot nice enough (though I don't have a crono for hard numbers), but after running a bunch of mags through, only the outside of the wheels have any dart debris on them. It looks like the darts don't touch the inside of the wheels.
If I were to do it again I'd pick 41.5mm or less to see if I can't get the wheels to fully contact the darts.
That said, I loved everything else about these, so I see a smaller size in my (near) future.
I got the 41mm cage to keep velocity below 150 due to local war restrictions, and running Fang ReVamps. This is a GREAT cage.
The print is very solid and high quality. I didn't need to sand anything, and just used an exacto knife to trim off just a few bits sticking out that'd interfere. The motors didn't require spacers and the cage fit perfectly into the blaster.
Once I got the wheels aligned and the cage balanced properly, my Spectrum shoots VERY straight. I'm not sure of the fps numbers, but by eye it looks very much like Kuriyaka's reported 140 fps (for 41mm spacing). I'm definitely going to order a 40mm setup too for use in the higher capped wars.