Sapphire 5850+S1v2 user here.
Fitting the heatsink: Yes, you need to bend the lower 4 fins on the S1, or cut them off. Not a big loss. There's also that guy who removed the DVI Heatsink on his card, but IMO bending the fins is simpler and faster.
About the VRM: If the VRM goes above 130, the card throttles itself back to 550mhz.
With the heatsink only and no fan at all, I only tried a stream app, and it rose to 90c and quit in about 5 minutes. This is in a case with semi-decent airflow. Semi-decent because I don't have intake in the upper bay, only in the lower one as all my HDDs are there - on the flip side, there are no cables getting in the way of airflow, even the front panel connectors I've managed to hide in the small space below the floppy slot.
Either way, running a 5850 + Accelero S1 with no fan is definitely not a good idea.
I had a 12cm Thermaltake fan running on 5v, mounted to the middle fan bay of the Antec P183. It fits extremely tightly, and it's probably not too healthy that way for the videocard since a lot of force is exerted on the 6pin connectors, right at the back of the card. With this setup, I got around 90c max gpu temp with furmark, but only because the VRM hit 130c and kept scaling back the card every other second.
After downclocking the card to around 700mhz (stock is 725), the VRM stayed just below 128c, though the gpu managed to hit 95c. 675 mhz got down to just around 90c for the gpu.
I didn't test games, but I tested an app that pushes gpgpu stream processing to the max, and it stayed just below 90c gpu and 120c VRM. (the app is self monitoring and shuts down if it reaches 90c on the gpu - in the half hour it was running, it never shut down). Since I use this app often, downclocking was not good, as performance got noticeably worse.
Idle temp was around 40-50 for the gpu.
Obviously, this solution was no good. I'm not about to burn out a card I bought for 300$ just this weekend.
So, I mounted the fan directly on the heatsink. It's held there by a couple of paperclips, so it's not exactly tight, but it's very close to the heatsink. A rather barbaric method, but I didn't have any other tools at hand (and I've no idea what else I could do to mount it anyway! Hold it there with female screws on one side, and a regular one between the fins?).
With the fan mounted directly, I get 72-75c gpu and 116-119c VRM in furmark. Idle gpu is 38-41c. I've yet to test Stream apps yet, but I doubt they will break 70c gpu. I expect games to run between 60-70c as well, maybe even below 60c. And it's silent enough that I can't hear it next to the HDD noise. Outside the VRM temperatures, I am content with this setup, for now.
In comparison, when playing games, I got as high as 77c with the stock cooler, and it got pretty damn loud even though the fan was only running at some 30%. Sadly, I didn't take notes of the VRM in the stock cooler. It would've been important, since the stock cooler covers the VRMs better. I'll probably buy the Thermalright VRM R4 to keep the VRM down from the ludicrous 117c on full load. The heatsink part of that thing should end up near the cpu fan, so even if I leave it as-is, it should have some airflow there (in case the big-ass heatsink alone is not enough to calm the raging VRM).
But, as it was pointed out in this thread, perhaps I could use the base of the stock cooler to cool down the VRMs more. At any rate, the ram sinks included with the Accelero are worth fuck-all for VRM cooling.
grandpatzer wrote:1. I'm getting a bit nervous for applying the cooler, almost wish I would have bought a used 4890 for more then half the price hehe.
2. Anyone know any good site or video where they explain in big detail removal of the cooler.
1. 4890 doesn't have DX11, and I'm sure you'd have temperature issues there as well, if you used just an Accelero S1 and nothing else. IMO the 5850 is the best bang for buck right now among hi-end videocards, considering its feature set and raw power. The 5870 pricetag is unreasonably high compared to its performance over the 5850.
2. There's nothing special about it, just unscrew it carefully. On my sapphire 5850, there are also two small screws on the side, next to the dvi outputs. Also, there are some smaller-than-average screws holding the gpu backplate on the card, so make sure you have a very small screwdriver for that.
(edit: the draper screwdrivers posted above are what I used as well, but only for the few extremely small screws, since that screwdriver set has the excellent habit of tearing the skin apart from my fingertips).
edit 2: To clarify, the 32c idle gpu I got was right after booting. Now that the system has "warmed up", I get around 38-40c.