-Intel i7-930 Bloomfield, 2.8GHz
-EVGA E758-A1 3-Way SLI (x16/x16/x8) LGA 1366 Intel X58 ATX Intel Motherboard
-CORSAIR DOMINATOR 6GB (3 x 2GB) 240-Pin DDR3 SDRAM DDR3 1600 (PC3 12800)
-Western Digital VelociRaptor WD1500HLFS 150GB 10000 RPM SATA 3.0Gb/s 3.5" Internal Hard Drive
-EVGA 896-P3-1255-AR GeForce GTX 260 Core 216 896MB 448-bit GDDR3 PCI Express 2.0 x16 HDCP Ready SLI Supported Video Card
-CORSAIR 750 Watt power supply
-2x Sony Optiarc 24X DVD/CD Rewritable Drive Black SATA
ANYHOW. I'm considering making two system upgrades. The first is that I would like a new Hard Drive to keep as a slave media device, so as to keep the VelociRaptor as a purely gaming/boot drive. I'm also considering an upgrade in video card, either purchasing a second of the same card and SLI'ing it, or selling my current card (or something) and then purchasing one of the 400 series cards.
So my questions are these. If I am to upgrade, and install a new video card and hard drive, would I also need a new power supply? if unsure, how might I calculate the required power to run my machine? also, would I be OK with SLI'ing another card, or should I upgrade because these new cards are that good?