can i use e8400 for 1 year or 2?and does it perform good later?
A CPU has the same performance throughout its entire lifetime. The reason CPUs seem to slow down is that software gets more and more complex as time goes on. Whether or not a CPU will delvier adequate performance for you a year or two later depends on your definition of "adequate performance" as well as what software you run. The 2.8 GHz Pentium 4s from 2002 that I use at work give adequate performance with running MS Office 2003 on Windows XP despite being 8 years old, because MS Office on the old Windows XP OS doesn't take a lot of power to run well enough. On the other hand, I personally wouldn't bother with buying any new desktop quad-core CPU for video encoding as they would still be slower than I would like. I would only look at a dual-CPU or better workstation setup for that purpose since video encoding is extremely CPU-intensive and heavily favors a lot of CPU cores.