After a long shipping delay, my Accelero S1 rev2 finally arrived today. I spent about half an hour installing it on the X1950 Pro. I used the pre-applied Arctic Cooling thermal paste on the S1; no need to get out my AS5.
AC has made some changes to the mounting hardware that's not yet reflected in their installation manual. The plastic clips for the top edge of the card to the heatsink are no longer L-shaped brackets. Instead, it's a block that you slide over the edge of the card, between it and the heatsink. Then you thread a long thin black post right through the HS fins until it clicks into the block. So instead of clamping on to the card from the outside, with a (weaker) angled bracket, it's a straight-through-the heatsink affair. I like it, though the snaps make it almost impossible to get off if you slide it between the wrong pair of fins. Make sure that the block is snug against the edge of the card! I had to redo one block, as it was one fin too far, and provided inadequate support.
I didn't use any of the included RAM sinks or misc. coolers, as the OEM RAM/MOSFET/etc. wraparound cooler is sufficiently low-profile, and works just fine. This way I don't have to worry about AC RAM sinks falling off as other users have reported. The downside is that one of the clip-on blocks has to be shoved out to the front of the card, partly biting on to the card, and partly on to one of the Crossfire connectors. Because of the block's design, it can't squeeze onto the main body of the card at that end. The wraparound RAM sink goes too close to the top edge of the card at that end, forcing the clip-on block to a slightly less secure position than the one at the opposite end.
But, since I have no intention of running Crossfire, this isn't really a problem . . . as long as that Crossfire connector doesn't snap off!
The Accelero + card fit just fine in my Antec Solo. There's a fair amount of compression and crowding at the power cable end. The 6-pin cord and cooler itself nudge up against top and middle suspended hard drives. The bottom drive is out of the way. I imagine right-angle SATA cables would relieve some of the crowding; it's a tight fit with standard cables.
I rebooted my system -- no heat-related shutdowns in the first few minutes the way some S1 users have recently reported. Now, I don't have any accurate temperature sensors besides the CPU core temp. There's a sensor chip on the graphics card itself, but as far as I know there's no way to access it (yet) under Linux. IIRC, not even Catalyst Control Center for Linux has temperature readouts. So I've stuck with the FOSS xf86-video-ati driver, version 6.10. It does support dynamic clocks, so it has some power management.
At first boot, the CPU temp read 24C. This was with both 120mm Nexus fans on the rear exhaust and Ninja running at 5V. The front-mounted 92mm Nexus in the top slot was running at about 12V. After a few minutes, temps crept up to 25C. When doing any light desktop work (all 2D), temps are around 26 to 27C. I turned the front fan down to minimum, and temps are generally in the same range, now and then drifting up to 28C.
This is perhaps 3C higher than idle/light load temps for the previous card, the passively cooled nVidia 7600GT (Gigabyte SilentPipe II), with about the same fan speeds. That's pretty good, considering that this is a higher-wattage card. The "official" graphics card requirements chart
lists ratings of 24W-36W-66W
for the X1950 Pro, and 15W-23W-36W
for the 7600GT.
Now, I've only had the S1 and card installed for a few hours, but already I'm extremely impressed. Blissfully silent computing.