Not to be pedantic, but the E8400 was very early 2008, being in January (the only reason I remember is because I bought one on release as that was when I finished my first PC). E8500/E8600 were later though, around when you said, yeah.
But yeah, I don't want to detract the thread too far off topic, but I thought I remembered Crysis being more thread limited and not quite taking full advantage of dual cores as it was, let alone quad cores, so your comment surprised me a bit. Around the time Crysis began development, CPUs would have only started gaining cores, and the writing wasn't yet entirely on the wall that single core speed scaling would soon slow, so it was likely developed like older games where they thought that future, faster CPUs would partly take care of the game's demands, and that... never quite happened. If I'm not misremembering (it's been years and years since I messed with configuring settings files for the game), it was more seen with the "very high" settings (or manually increasing draw distance in particular, I think) that really asks a lot of the CPU, and that isn't helped with extra cores. Even relatively recent-ish CPUs can have frame drops below 60 FPS due to lack of single core speed in that game if settings/draw distance is high enough. There was some stuff that was split to different threads (like AI) but otherwise I recall it specifically being single thread limited. Even the remaster has much of the same issue I think.
Crysis 2 and 3 (being developed on CryEngine 3 instead of CryEngine 2, and being more multi-platform developed with the multi-core consoles partly in mind) were a bit more multi-threaded I think. Perhaps you're thinking of either of those?
A higher resolution in the game should only increase GPU needs, not CPU core count needs? So that part confuses me (although something like the then-new 16:10's wider FOV would need a bit more CPU than a 4:3 FOV, but again that would mainly need more single core speed). More cores would help with background tasks, yeah, and I can imagine a shop wanting to use the latest games/multi-tasking scenarios as ideas to want to upsell people in general (not shaming with this statement, just proposing it as a hypothetical possibility as to why you may remember that experience from that situation?).
But yeah, regardless... it was a fun and pretty game so now I'm kind of sad it isn't working for me at the moment but I'm also not looking to play it right now. If I ever want to play it again, I'll look into workarounds.
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The game is much more fun in co-op, especially when you're under-powered. I met some really nice people there. Killing bosses is sometimes a chore to get done all by yourself.