Hello khromosone
From what i could gather on forums, the 4870 is by no means a very cool card so trying to cool it with the S2 would not be advised and anyway it does not seem to be compatible with the series :
http://www.arctic-cooling.com/vga2.php?idx=125
The Accelero S1 is a better cooler but do not expect to run it passively on a 4870. Even on a vanilla 4870 it seems to struggle with a very low airflow fan.
Your 4870 is an overclocked version...
And cooling other components like RAM and especially VRM is just as important on those power-hungry cards so you should take that into account and check where you would need additional heatsinks.
Even after all this, Xpert seems to be using a proprietary PCB design so you would need to ask either Xpert (Palit) or Arctic Cooling about possible changes that might have been done to the mounting system/design that could prevent compatibility with the S1, even if AC website states 4870 are compatible :
http://www.arctic-cooling.com/vga2.php?idx=147
You could also consider the AC Twin Turbo that is also listed as compatible with 4870 and with which people seems to obtain reasonable cooling with reasonable noise levels. Then again, check the compatibility sections on those pages to ensure your specific card could be compatible.
http://www.arctic-cooling.com/vga2.php?idx=166
Other high-end coolers you might consider also include the thermalright T-RAD2 :
http://www.thermalright.com/new_a_page/ ... trad2.html
and the Scythe Musashi
http://www.scythe-usa.com/product/vga/0 ... etail.html
will are also listed as compatible with the 4870 series and are quite performant coolers as well.
All previous restrictions mentionned above still apply for those products. With all the others above, those constitute the most talked-about coolers from a silencing point of view. Do not bother with other blingy-er products like those from (insert other less reputable company particularly loathe on this forum).
Of course, apart from the twin turbo and musashi, all those products will only be as quiet as the fan you use with them (they are not included with others) and the way those fans are controlled. It might need a bit of tinkering/trials and errors to determine the optimal noise/cooling compromise. As far as i know, no current cooler can deal with a 4870 purely passively.
Also remember all products listed as compatible do so on the basis of the standard 4870 specification by ATI. 3rd party companies can modify those so there is no guaranty a cooler can fit your specific card. But on most companies you can download some compatibility list/height restrictions/product manual that might help you determine if you could use it.
Oh, and by the way, you do know you are voiding your product warranty if you are swapping the cooler right ?
Just to be sure.
And i also remember there was some people mentioning only one of the two fans was controlable, the other being on full-speed at all times. Disconnecting the culprit did not seem to change temperatures too much but you will have to do your researches on the matter. You still might want to look into that to quieten down the card without voiding your warranty (or at least not making it too obvious). Or maybe you could find a 3rd-party utility like RivaTuner that could help you set the fans lower that the driver itself allows. That might help at idle states if temperatures are not too high then
From what i could see with a quick look at google images, a fan swap would not be too easy so i would not recommend that route.
To sum up this long answer to a old-ish post, you need more information, particularly on the changes to standard specs done by Xpert to be able to know what 3rd-party product might suit you. Or maybe you can find some software tools to help you modify fan speed profiles are the driver or BIOS levels to quieten down the existing cooler.
Hope it helps and happy tinkering.
