I had this same question myself (2.6 v 2.7) and concluded (for better or worse) that the +2mb of L3 cache wasn't worth $150. My inner nerd kinda wishes I got the 2.7, but when i go out for a fancy dinner sometime soon with my lady, I'll just tell myself: this is in exchange for 100mhz and 2mb of L3 cache. And I sure as heck am not gonna change order and wait an extra month at the back of the queue haha.
I think honestly the 2.9 is probably not worth it at all though. The other 2 are arguable. I'm sure it'll make some milliseconds of difference in your life. Maybe you'll even waste an hour over the course of 5 years, waiting for L3 cache paging to occur. Who knows?
But in the end, it's all just time. Time spent waiting on rendering. Time spent obsessing about configurations.
They're all great processors.
Def get the GPU upgrade though, as everyone has been saying.