I'll be honest, I'm still using Crunch3r's 5.5.0 SSE2 optimized client. However, now many projects are banning/trying to stop optimized clients (latest I've seen is HashClash), thus I'll claiming a high amount of credits but only being grated a low amount.

I'm wondering what version everything is using so I can upgrade. I'm thinking of trying out BOINC 5.6.5 which is hidden in the BOINC servers for downloads.
http://morel.mit.edu/download/boinc/dl/