From all of the time I have spent playing Blizzard's wonderful games, this is the first post that I am actually creating on the Battle.net forums.
To get right down to business, with the release of Diablo III, as much as I and many others may be enjoying the game, there will always be performance issues on release. Even if a game took approximately 12 years to make. That being said, Blizzard over it's 12 year development has chosen to code Diablo III with a "steaming" type of engine (the fact that certain files, in this case, the .mpq assets must be constantly read from the hard-drive in order for the game to function "properly"). Unfortunately, this combination of code has lead to many woes for many gamers, including ones with high-end PC gaming rigs. This issue has become known as the "Loading Assets Issue" . While there may be a lot of temporary solutions posted on these forums thus far, I would like to post what may be a permanent fix which may apply not only to this game, but to everything you may do on your PC from now on.
Look into Windows Cache optimization solutions. Two of the biggest programs (yes, they are shareware) that I can think of are Raxco's PerfectCache, and O&O's CleverCache. Basically, these types of programs optimize your file cache management in Windows. This results in an enormous performance boost, sometimes doubling your original system speed without any additional hardware purchases or restrictions to your system’s stability. If a computer is used without interruption for longer periods, slower answering times of applications will occur. By restarting the computer, you will find out that the system runs with significantly higher performance. The reason for this is the empty file cache resulting from the reboot of the system. These programs achieve the same result without any reboot, ensuring maximum performance while the system is online. To some extent, some may say it performs just like a RAMDisk, but the difference is that the important files that are being utilized at a specific moment are the ones being taken care of right away, unless otherwise specified. I have recently installed O&O's CleverCache, and I must say, virtually ALL of my stuttering problems that I suffered before, are gone. The only "stutter" I get now is when the game actually loads up for the first time.
My System Specifications
Operating System: Windows 184.108.40.20601 (Service Pack 1)
CPU Type: Intel® Core™2 Quad CPU Q6700 @ 2.66GHz
System Memory: 8.00 GB
Video Card Model: NVIDIA GeForce GTX 560 Ti (Twin Frozr III) 301.42 Drivers
Video Card Memory: 1.28 GB
Desktop Resolution: 1440x900
Hard Disk Size: 2TB (2x1TB RAID0)
Download Speed: 50 MB/s
With the system mentioned above, I have been going from 150+ fps to 20 CONSISTENTLY. It never stayed in one place because I always was in the middle of big action. After the fix, without VSYNC, I maintained my 150 fps through out. The game really did feel fresh, as it should have during launch.
TL;DR: IF YOU ARE HAVING A SEVERE LOADING ASSETS ISSUE, GET A PROGRAM THAT WILL BETTER MANAGE YOUR WINDOWS 7 FILE CACHE. DOESN'T MATTER IF IT IS FREEWARE OR SHAREWARE.