Tom's Hardware is where I usually go when looking for benchmarks. They have many cross-manufacturer and cross-architecture benchmarks, which really helps to compare processors where it would otherwise be apples to oranges. While they tend to be a bit more gaming-focused, they do run the usual array of generic benchmarks. Googling around for additional benchmarks is my next resource if I'm still on the fence.
The problem is beyond benchmarks, there's still several things which are hard to quantify (such as the ability to over-clock. I absolutely love Intel's Core i7 series, because I know that I can take the 2.6GHz processor up to somewhere in the 3.8-4.2GHz range with minimal work). I compensate for this as best I can by simply keeping my interactions with different processors varied (using them at school labs, specialized labs, etc.) to discover architectures that perform well across the board. If you look on the other side of things, you're more than likely to replace the processor in a year or 3, so barring any actual problems with the processor, slightly-less-than-optimal-performance-than-what-you-could-have-gotten is not something you have to live with long-term.