If you are not doing a lot of rendering and transcoding of video, then 1156 will do.
The 1366 has 1366-1156= 210 more pin-outs. Most of these are data lines so, tho the die is essentially the same for an 1156 i7-860 as for a 1366 i7-930, the amount of parallel data that can be "pumped" on and off the cpu is ... that much more.
Platform longevity does play into it. Figure that , with another $300 cpu (and prolly a ~200$ gpu), added in about 3 yrs, you may be able to almost doubly extend your longevity.
The other route is to spend less now and "run it into the ground", replacing everything but the CASE & PSU, in 3.5 yrs, or so.
I kind of splurged on a 2.8GHz P4, 5 years ago, and traded that off to a buddy so I could get the 3.2GHz P4 I am using on this system. This is still a very viable general purpose system .... I even put a $130 nVidia7200GT(OC) in it (much cheaper after those few years) and a few more sticks of ram. All that was 2 years ago and the only place I am really feeling much drag is with long video output renders that can take 7-12 hours (at the very highest quality 1080P/30 25Mbits/sec CBR 2-Pass) ...
I have been considering a 1366 for that reason but I have decided I'm gonna try to limp and suck air untill the PCIe3.0 bus standard comes out, in about a year.
What that means, for me, is that I will be focusing on editing that huge crate of standard definition DV-25, VHS, SVHS, and Hi-8 videos ... as well I should ... even tho HDV 25Mbit/sec footage is piling up on me fast.
So, this year, I will continue to SHOOT in HDV (accumulating Art footage), but I will be editing a few years of backlog.
This sort of makes economic sense because proc power is just now catching up to consumer HD codecs. Another year and that power will no longer cost a premium.
You have to watch product cycles and realistically project your "proc power needs" over the amortized life of the system, be that 3.5 years or a very long six years (few pcs last 6 years without major overhaul).
The good news is that all that speed and power is cheaper than ever and will trend that way. If you NEED to upgrade, now is the time (always) ... The matter of how substantial an investment you should make in "robust" system architecture really does take some sussing (after lots of research).
For 3.5 year commodity/appliance grade computers ... you just get one when you need it ... not going much beyond current needs.
Some people feed at the trailing edge (as opposed to 1st adopters) and can cobble an aging platform together out of used parts, but have to do that pretty often.
I think the AM3 socket (Latest AMD) with a fast 3-core proc and 4GB ram is a very reasonable medium, in terms of power, and will save you big-time, on price.
Try a build with an AMD/AM3 Phenom-II Triple Corre and 4GB of fast (CAS 7) RipJaws DDR3 ... Drop in a 64GB SSD as your boot+apps drive ($150) and a Samsung Spinpoint F3 HDD (~60$) for media content. It will scream ... Overclock it and LAUGH at INTEL owners ... It's like Levis vs Jordache.
= Al =