I'm with Tod, in that I don't really do RP stuff or combat, but I easily could. I create SL content for a living, and when you do that all day long, you have to run as lag-free as possible. Generally I get 25-40 FPS on the mainland, and mid double to sometimes as high as low triple digits on islands, depending on what's around. That's at 512 draw, all graphics options enabled and maxed, and 16xQ anti-aliasing.
The highest I've ever gotten is around 130 FPS on a relatively clean island, but that was pre-Windlight, and with SLI running. I don't generally use SLI, since I use dual monitors, and I haven't tested to see how high I can push it with Windlight. (And before anyone jumps in and says "But SLI shouldn't make any difference for SL", which always happens whenever it's mentioned, I can promise you from experience that it does. Perhaps mileage varies, or perhaps the people who make that claim have just never tested it. All I know is I get about a 30% boost in FPS with SLI running.)
Here are my relevant specs:
OS: Windows XP Media Center 2002 SP2
CPU: Intel Core2 Extreme (quad) QX6700 @ 2.66 GHz
Memory: 2.5 GB high performance DDR2 RAM
Video Cards: (2) nVidia GeForce 8800GTX w/ 768MB DDR3 vRAM each
Motherboard: nVidia 680i SLI motherboard
System Drive: (2) WD Raptor 150 GB 10,000 RPM on RAID stripe, for double read/write speed
Data Drive: (2) WD Raptor 150 GB 10,000 RPM on RAID mirror, for continuous redundant backup
Scratch Disk: (1) WD Raptor 150 GB 10,000 RPM
Other Disk: (1) WD Caviar 500 GB 7200 RMP in external housing, connected via eSATA, for manual backup and file portability
PSU: Tagan 1100W Power Supply
This stuff is all about 18 months old at this point, so it's last generation now, but it still kicks ass. It's not all that expensive to put a rig like mine together these days, or if you want to spend a bit more more, I'm sure a comparable setup with current components would do even better.
One thing to note is it's not just the CPU, RAM, and video card(s) that make a computer fly. Your hard drive setup has a lot to do with it too. I highly recommend Raptors, as they're the fastest and most reliable drives on the market. They're pricey, but well worth it, in my opinion.
Having a dedicated scratch disk makes such a difference for keeping your system drive running at full speed. If you have your SL cache, Photoshop scratch disk, etc., on your system drive, things get fragmented very quickly. But with all that stuff on a physically separate, dedicated drive, your system drive stays at peak operability for much longer periods.
Also, it's not all about the hardware itself. How you use it and maintain it to keep it healthy makes all the difference in the world.
Weekly defragmentation of all drives is a must. It's like changing the oil in your car. You have to do it, no matter how good or bad the car is, or you will have problems. I recommend getting a good third-party defrag program, like Diskeeper or O&O Defrag. The built-in Windows defragger really sucks.
And of course, do everything in your power to keep your system free of malware. Regular sweeps for viruses, spyware, adware, etc., are absolutely vital. If you're not already in the habit of doing that, you'll be amazed at what you'll find running on your system that you didn't know about. "Drive-by" installations happen all the time while you're Web surfing. That stuff really slows you down.
Also, get rid of any extraneous processes you don't need. Software companies love to put useless little extras in, to run alongside their stuff. Things like the Quicktime helper, iTunes helper, Windows Messenger, etc., just sit there, wasting memory and CPU cycles for no good reason. Individually, none of these will make or break your performance, but when you add them all up, the impact can be huge, especially for a program like the SL Viewer, which gobbles up every ounce of available resources when it runs.
Make it a regular habit every day to take a look at what processes are running. The Windows Task Manager will give you a general idea, but it's not terribly informative. Process Explorer is a pretty good freebie, which will tell you a lot more. If you don't know what something is, look it up on the Web and find out. If it's not necessary, get rid of it.
And one more thing, the OS makes a difference. XP will run all OpenGL applications, including SL, faster than Vista will. The flip side is that Vista, of course, will run Direct3D programs faster than XP. Bit since since we're talking about SL here, and since SL does use Direct3D, that really doesn't matter. OpenGL performance is what's relevant for SL.
I hope that helps.
