This is only my opinion about Mac Pro Single Processor "Sandy Bridge-E". Assume: 1.) Next SP Mac Pro will use this line up. 3.6 Quad Core Xeon E5-1620 3.2 6 Core Xeon E5-1650 3.3 6 Core Xeon E5-1660 2.) Sandy Bridge-E and Sandy Bridge have identical clock-byclock performance but different on Memory , I/O Speed and etc. Evidence:  http://www.barefeats.com  http://hwbot.org/blog/wp-content//sandybridgee-results.jpg  http://www.xbitlabs.com/news/cpu/di..._Boost_Performance_by_Up_to_65_Estimates.html Analysis: - E5-1620 will be faster than i7-2600K ~ 5-6% on both Multi-Threads and Single-Threads according to it's faster clock - E5-1620 will be faster than Xeon W3680 ~ 10-15% on Single-Threads and On-the-par on Multi-Threads according to iMac Testing + 5% that E5-1620 faster than i7-2600K  - E5-1650 faster than Xeon W3680 ~ 4-5% on Single-Threads and ~5-10% on Multi-Threads according on  - E5-1660 faster than Xeon W3680 ~ 8-12% on Single-Threads and ~10-15% on Multi-Threads according on  - E5-1620 will be faster than E5-1650 ~ 4-5% On Single-Threads and ~15-18% Slower Than E5-1650 on Multi-Threads according to it's faster clock. - E5-1620 will have same speed with E5-1660 On Single-Threads and ~20-25% Slower Than E5-1660 on Multi-Threads according to it's equal turbo boost. My Bottom Line: 1) Mac Pro vs iMac : If you consider to buy an iMac or Mac Pro. Next Entry-Level Mac Pro will 5-6% faster than Top-of-the-line iMac. 2) WAIT For Entry-Level Mac Pro Buyer : You will get ~20-30% Performance boost with 3.6GHz Quad Mac pro. (VS. 2011 2.8GHz Quad Mac pro) and on-the-par with 6Core 3.3GHz Mac Pro in Multi-Threads situation. 3) For 6-Core Mac Pro : If My Assumption are true you will be get 6 Core system much cheaper.