Thanks for the suggestions. I guess my issue is that it's hard to justify putting another couple hundred into the RB when I can get the RZ for such a good price.
If I can swing getting the RZ (with 90mm or 110mm) and a 50mm lens before the job, would that be more advisable than getting the 50mm for the RB? I think I may be able to get it with the KEH prices. Is there any reason NOT to go the RZ route?