Firstly, there is absolutely NO point in getting an AMD quad over a 955BE. They are all the same chips (besides the acclaimed never been seen 960t *cough*) and basically all OC the same amount. I recently did a bench off against a new 970BE with my i5 750 and i still won and my chip is over a year old now. =/ If you wanted to spend the cash, get either a 955BE (or i5 750 setup) or the 1055T. If not, then the 555 should work if you can overclock it high enough.
Now thats taken care of ill fill you in on some performance issues nobody is mentioning yet. Firstly, SLI on a 1680x1050 screen is kinda wasted. A more powerful card would be more beneficial to your resolution because SLI/Crossfire is more for resolutions like 1920x1080 ect. For performance figures SLI 9800GTX+ is about equivalent if not sometimes more powerful than 280. Upon recent benches my highly overclocked 465 is only a notch more powerful than my old 280 but with DX11 support. A GTX285 for so cheap would be (IMO) your best bet out of all options. I say this because its still a very powerful and capable card, and there arent really any "true" DX11 titles yet except maybe Metro2033. So on the video card front id say either that 285 if you can, or a 460. Either way is a great option.
Next, please oh please do NOT get an Nvidia chipset AMD board. I used to be a huge fan of them but after i reviewed a 750a, then 780a, and finally about 6 months later a 980a ive been highly disappointed. They are hot, not as quick as the AMD counterparts, and not really worth it for the SLI considering you can do the SLI hack on literally almost any board out there. (No seriously, want the link ill get it for ya).
Instead id recommend this for almost the same price.
Newegg.ca - ASUS M4A89GTD PRO/USB3 AM3 AMD 890GX HDMI SATA 6Gb/s USB 3.0 ATX AMD Motherboard
You will have almost a top end board on the AMD front. (Yes i used the CA site)
On the same order you can spare that extra cash you need for the board by getting these instead for RAM
Newegg.ca - Mushkin Enhanced Silverline 4GB (2 x 2GB) 240-Pin DDR3 SDRAM DDR3 1600 (PC3 12800) Desktop Memory Model 996947
Finally to trim a few more bucks off your purchase you can get this SSD instead with TRIM support with the same Sandforce controller for the same speeds one would want with a fresh gen SSD.
Newegg.ca - Corsair Force CSSD-F60GB2-BRKT 2.5" 60GB SATA II MLC Internal Solid State Drive (SSD)
If you wanna go cheaper the G.Skill Phoenix Pro will prolly perform about the same.