Somehow I could never get my SB 900 to overheat. I did a stress test for 2 minutes with newly charged eneloop batteries; using the test button as soon as the ready light was illuminated, I never reached the flash to overheat. It might help out if you use ISO 400 instead of ISO 100 and minimize using f8.
One of the forum member conducted a test using two seperate sets of batteries which includes the immedion and powerex 2700mah. The powerex started to overheat after 42 consecutive shots as soon as the ready flash indicator was lit. The Immedion batteries reached thermal shutdown after 50 consecutive shots. Recycle rate is 2.3 seconds with the SB 900.
I don't know how demanding your flash photography requires but if you stay within the recommended flash rate, you shouldn't have any problem even for wedding photographers.