Yes, I gave my GPUs a 5 minute cool down period near the end of the round. I don't think that deserves the loss of nearly all rewards from almost 2.5 hours of mining.
Just trying to be objective and helpful here. But I guess you could...
I appreciate your helpfulness. My cooling system is about as windy as I can make it, but I like to overclock to within the limits of it's heat transfer capacity. I'm trying to avoid going the liquid cooling route. I often do seize the chance for a cool down at the end of a long round, but when they peak up to 98C and there's no telling how much longer the round is going to be, I feel I don't have a choice. Only takes a couple minutes to get them back down to 40. After a cool-down period of my own, I find myself not really liking the waters in the Guild's pool, and as mentioned, most other pools either have the same scoring system and/or higher fees. While invalid blocks and scored out rewards give me the blues, I'm still jumping right back into Slush's pool.
Why are you clocking your cards so high? Find a happy median between heat and hashing and stick with it. I have plenty of boxes that have ran non-stop for months without ever looking at them. Are you giving the cards too much voltage?
You do realize that letting your cards heat up and then cool down is WAY worse for them than just letting them run hot right? 98C is simply too hot, pull them back into the 80's and you'll be golden. Personally I don't run much hotter than 80C if at all possible and find the clock and voltage settings to make sure that happens regardless of ambient temps.