Er...that's hard to say because parts/manufacturers vary but its pretty rare for higher quality stuff to go bad earlier. With your stuff, I think it will all still be running in 6 years even overclocked.
If you had ECS mobo, VIA chipset, value RAM and a cheap PSU, then you'd have problems.
As a side note, I too have the P35-DS3R with a E6420 (stock fan). I've played around with just upping the FSB and leaving the BIOS to auto everything. 390 ran SuperPi but 400 crashes.
I will try the advice here as the temps were only 37C but I think the auto voltage and memory timings need to be manually adjusted by me.
Re: wanting to overclock my E6420 
Linear Mode
