I actually have the S2 $17 on my 8800GT. At stock speeds while playing Hellgate:Lodon(MAXed 4xaa 1280x1024) for half-hour~hour it maxes at 74C. Stock cooler would go way above 80C even with the fan. Idles around 48C, stock cooler would idle @ 60C. I'm getting the turbo module fans in today ($8) @ EGG and I'll let you know how cold this thing can get. Also installation is a little tedious, not to bad though. Make sure when you install it that you put the plastic L clips closer to the ends of the card. I accidently put them to close together and knocked one of the memory sinks off. With a small screwdriver and some amazon like skill I was able to restick it back on the memory. also in the final step when you click the T clip to the L clip you have to have good pressure on both ends, eitherwise the L clip will pop off the card, Its not hard, its not easy, just needs a little skill
My stock cooler idles at 48C. Guess you dont have really good airflow in your case?
What type of cooler do you have, they recently released the 88Gt's with better options now, also whats your fan setting, Every person I have read from usually had there 88GT idle @ 60C +/-5C. Do you have the side of your case off with a fan blowing on it? My case has an 80mm intake. A 120mm exauhst in a double pull setup with the 90mm on my CM TX2 HSF as well as the 120mm fan on my thermaltake PSU sucking some of it up and out. So case cooling is very solid in my case...get it my 'case' MUAHAHHAA. But really please explain your setup. To get idle temps of 48C On stock HSF with no settings/mods is nice.
Also forgot to mention I DID get the turbo module from the EGG and installed it. All I have to say it wow. Idle temps right now from RT are 38C. Load temps (HG:L after 30minutes+ max settings 4xAA while recording temps with RT chart in backround 49C max, and I do specify 49C because there wasnt a part of the chart I scanned that hit 50. Now thats bad ass for another $8 + shipping. Not only that I have one of the fans blowing down on all the various non-GPU-MEM compenents, I think they were the VRM's and such.
Got the S1 with turbo modules inbound for my BFG 8800GT OC2. It has 4 heat pipes instead of 2 and a larger heatsink surface, so it should offer slightly better temps than even that (though what's the point when you are at 38C/49C on a graphics chip!)