I have a budget of around 1500 for a good used 1 or 2 year old workstation. I'm considering an HP Z600 or Z800, but I do not know if I should go for the X5560 Nehalem (2009 high end 45nm) or E5620 Westmere (2010 middle grade 32nm) CPU.
the x5560 benches higher but I've been reading that newer CPU's perform exponentially better.
The x5560 is better, doesn't matter if it's older. Westmere was just a die shrink of nehalem and there wasn't much of a performance increase. Infact these tests show next to nil. (Look at the i7 970 westmere vs i7 960 nehalem. Although take into account it is 6 core westmere vs 4 core nehalem.) http://www.tomshardware.com/reviews/cpu-performance-com... Even giving it a 20% performance increase per clock (which it wasn't), it still would not make up for the lower speed.
after some research I decided that the processing power of my Thinkastation D10 with dual x5482 (harpertown / Penryn architecture) still outbenches a single x5560 or e5620 on both cinebench and cpumark.
I think I'm going to wait maybe another year and save up another grand and get a dual x5680 system (2x 6 core westmere), which truly is over 2x faster then my current system.
Thanks for all the great advice guys! for now I just spent a few hundred (gotta love ebay!) on a quadro 4800 (currently have a 4600) and 32gb ram to hold me over