Thanks for advice Primo. Gonna try to decrease resolution and check if lag remains. Also, how do I check CPU usage while playing? Because if I alt-tab CPU usage instantly decreases and I don't have double monitor.
You have 3 options to check the CPU usage:
1) Check the Task Manager's graphs for each core and estimate what was the CPU usage just before you alt-tabbed;
So I need a little advice. I got i7 920 2.67 Ghz CPU and HD4890 GPU and I still have some lag in beta when there are big battles. I am just wondering which piece of hardware is lagging here? If I know I can overclock it.
Overclocks generally don't give much more than 10% performance gains, what means nothing for gaming.
I think the problem may be physics running on your CPU. Although I'm not sure how they implemented physics in game, IF it uses only Physx to run it on GPU, the game is processing the physics on your CPU, what may overwhelm it in some cases.
To be sure, you can keep an eye on your CPU usage when these big battle are happening to see if it's near 100%. When doing it, don't forget that your CPU is a 4 core, but it has 8 total virtual cores. So, if 4 cores are near 100%, the CPU is giving all it can, even if the Task Manager indicates only 50% usage.
Another test you can do is increase/decrease only the resolution in the game options. If the game slows down much more when increasing it, the bottleneck is your GPU, because changing resolution mantains the CPU load almost intact.
If you find out the problem is your CPU, you may try to overclock it to 3.2GHz, maybe 3.5, but I don't think the standard Intel cooler will be able to maintain a nice temperature unless your ambient temperature is less than 20º C.
My machine likely support the game (win7, core i7....)
However, my video card, hd 5770, is lower than the recommended in the 3D mark, by say, this computer bought 1.5 years before is a bit out-of-date.....
Computers change rapidly
btw, I am interested how hard-disk affect the speed of loading because the only 1TB hard-disk storing the system are often overloaded.
But the HD 5770 is very close to the GTX 260 in performance. If your benchmark results were too low compared to the GTX 260 results posted, it may be the case where your CPU is too slow.
EDIT: I noticed you said "i7". Well, then I don't know why your results are low, but I'm sure the HD 5770 is equivalent to the GTX 260 for gaming.
About HDD's. With a single mechanic drive you'll have regular load times. If you put 2 on RAID 0 you'll have considerable better loading, about 150% the performance of a single drive or 60% to 80% the load time of a single drive.
Now if you use a SSD you enter into a new dimension.
I find it annoying the number of games that are lowering the specs (and visual quality) recently. A perfect example is DiRT 2 and 3. The last is clearly less demanding and "ugly" than its predecessor.
Now about Diablo 3, I knew Blizzard would not push the specs too much because... well, they never do that. I don't know if it's to reach a broader audience or what, but when you release a game that can run smoothly (at least most of the time) at max settings on 4 years old GPU's (GTX 260)... something is wrong with that. I think it will look "dated" long before the end of its life (Blizzard wishes this Diablo to be played for around a decade).
Even Blizzard's art department being really talented, games will look old if you're too "shy" on specs. WoW, for example, is beautiful, but everybody says: couldn't this/that "be more shiny"/"be shaded"/"have more polygons"/"have a better texture"?.
That's why I think every game should be released with an extra "ridiculously ultra" setting which is only able to run on 4 GTX 580's and an overclocked extreme CPU (or not even on that).