PCC, I really mean no offense (you know how I sometimes say exactly whats on my mind...
), but why upgrade for the sake of folding if you don't fold full time for the summer. For now your 4-core i7s are still a good option for the summer months. I understand it gets pretty warm at your location and in the past you have taken it lightly with folding during the warm months. At the end of the summer, it might be best to re-evaluate the options.
But then, sometimes, you just need to jump in and buy... instead of waiting... like when you wanted to buy a bunch of GTX275s back when that was pretty much the best option for ppd/$ or when you were pretty much set on getting the SR2 last year.
I got an i7 970 this past week, got it in doing bigadv in windows right now, and will work on some linux folding sometime when I'm not working 12 hr days. For me, it will definitely be worth it since I fold pretty much 24/7, 365.
I did already have plans to buy one before these 12 core units were announced. I will sell my 930 to make up some of the cost of buying.