I was using a phone the last couple of days and mixed up some of the numbers. I'm going from 52t to 48t, so I think thats about an 8mm reduction in radius. I also wasn't looking at the bottom bracket specifications correctly. I haven't dug out the RSX crank yet to confirm the exact model, but the Shimano literature is listing a 8mm bottom bracket difference between a double and triple RSX crank sets which is basically the same as the chain ring spacing, so that's promising.