After years and several rounds of upgrades, I run a high end system and am pretty obsessive about SL performance. I thought I'd spec out an ultimate SL system based on my experience. What you list is overkill on the CPU side, but underpowered graphically. This goes for most games - SL especially needs the fastest video card you can give it to max out its settings. Even then it won't be quite enough to completely max out everything smoothly at 1080p and up resolution. SLI and Crossfire in Second Life are pretty useless, so you want the fastest single GPU card available. You also want a SSD for fast zoning, and faster memory would probably also help. Based on my experience, here's what I would recommend for a price-optimized high-end build that's built specifically for Second Life, with everything you need and nothing you don't for the very best possible experience. Of course it will also be great for any other game, too! Prices are current on Newegg as of this writing.
CPU: Intel Core i5-3470k Quad Core (3.4GHz / 3.8Ghz Turbo) $229
Cooler: Coolermaster Hyper 212 Evo $35
Case: Antec 302 Black $68
Motherboard: Gigabyte GA-Z77MX-D3H LGA 1155 Intel Z77 $129
Memory: G-SKILL Ripjaws X 16GB (2 x 8gb) DDR3 1600 9-9-9 $95
SSD: Samsung 830 Series 128GB $119
Hard Drive: Samsung Spinpoint F3 1TB $85
Video Card: Galaxy Geforce GTX680 SOC White Edition $555
Power Supply: Seasonic M12II Bronze 620W $89
Monitor: ASUS VW246H Glossy Black 24" 2ms GTG 1920x1080 $179
Keyboard and mouse: Microsoft Comfort Desktop 5000 $59
Speakers: Logitech Z523 $79
OS: Windows 7 Home Premium 64 bit $99
Total: $1820
Obviously corners can be cut if need be to meet a price point, but this is a no-compromises SL system with no extra 'fluff'. I've been through several rounds of upgrades and learned a lot about SL performance. Currently I'm running a overclocked Core i5-760 with 12gb RAM, 128gb SSD, and a GTX670.
Hope this helps.