Upgrade Dilemma I7 vs new MB

I need opinions on upgrade cost considerations vs future proofing etc, on my i7 920

Here are the specs:
Thermaltake Armor VA8003BWS (Modded)| EVGA X58 Classified sli 760 | Intel I7 920 (non-overclocked)| Thermalright Ultra-120 eXtreme cpu cooler | Crucial Balistix 6gb DDR3 1600| Intel X-25M SSD 80gb | WDC WD6401AALS 640 gb | Sapphire Vapor-X 5870 HD Gpu | Antec TPQ-850 850W Quattro PSU | Claro Halo XT Sound Card |Klipsch Pro Media 5.1 Audio | Dell 2405 FPW Monitor | Windows 7 Ultimate 64bit SP1.

Im thinking if the 990x comes down to below $500 i should upgrade and squeeze a few more years as opposed to all new everything, this setup was built in Dec 2009 i think. i could upgrade ram and gpu much cheaper than new mb, cooler, ram, etc.

I might add the system is still pretty strong, but i'm noticing some slow downs in games etc, and think its getting slower in its old age, i know nothing about overclocking, so thats not a good option for me...Thanks for your comments.