Wow! That's a very thin wall section over the key. For an arm application, I would be cringing over it. For kit drive, I'd think it's borderline. We did the same think with the kit tranny last year, and it easily saved 2+ lbs per side.
However, I'll point you to a pic of our robot (or a part of our robot) after a slew of competitions. Beware of those thin walls!
228's shattered arm gear
Best of luck!
BEN