I have 2 systems with hd-4870's, one is the older reference cooler/card the actual radeon from ati. The other is a newer sapphire hd-4870, both are 512mb cards.
The older card runs much hotter in spite of its larger cooler, also it maxes out at about 780/950. I run it at stock clocks.
The newer card runs much cooler in spite of its smaller cooler, it also draws less power. It tested stable at ccc max at 850/1000. i run it at 800/1000.
-It is pretty obvious that there are two 4870 gpu cores.
-I can see in your screenshot that your core maxes out at 790mhz like my older radeon, the other card ccc maxes out at 850. So you have the older 4870 core, most barely passed testing as a 4870 core and most were sold as 4850's. It should run at 790mhz but 40mhz wont be much in games and you risk game crashes.
The fans on the 4870's run off of a temperature controlled pcm chip, so the more heat the gpu puts out, the faster and more noisy the fan will run. Overclocking will just make the fan louder under load.
-Do not run manual fan mode on modern cards, they need this temperature control on the fan speed to protect the card from overheating. I once had a case fan die and the card's fan sped up to save itself.
GtaIV is a cpu limited game, the 4870 even at stock clocks is already faster than the cpu in that game. you would benefit more from overclocking the cpu from 2.4 to 2.5 or 2.6ghz than clocking the card really high.
In my living room pc i am running the older 4870 at stock clocks and a socket 939 x2-4400+ firstname.lastname@example.org. It gets about 30fps @1080p in GtAIV. GtaIV is a stubborn game to make run smooth.
After having 4870's for a while i figured out some settings that seem to work and give you decent quality while having good fps. This makes a bigger difference than overclocking by far.
- To help out the cpu and prevent uneven framerates, select the "wait for vertical refresh" to "always on" so the framerate is capped at 60fps.
- Set the "Mipmap level" to "performance" at high resolutions like 1080p you dont need this set too high, this kills your fps.
- check the "enable adaptive AA" box and set it to "quality" this helps more than a high aa and af setting without hurting fps so much.
- set the aa to 4x and uncheck the "use application settings box"
- set the af to 4x and uncheck the "use application settings box"
- set the "catalyst A.I." to "advanced", some games use optimizations that help fps and quality.
Well good luck i hope it helps you out.