Boris,
I can give you a bit more specific information. A couple of HP machines with dual core 4200+ and 5000+ processors handled HDV from a Canon HV20 OK but nowhere near as fast as I was used to editing standard DV and miniDV. The rendering process (Produce or Create Disk in PD7) was somewhat slow, though, and if more than one "effect" was added to some clips rendering those took a lot longer.
When I started using Canon HF100's (AVCHD) things took on a whole different aspect. The HP dual core 5000+ could just barely do it if the camera quality setting was taken down from 1920x1080 to 1440x1080 but was agonizingly slow and for me unworkable.
My (then) new quad core Q6600 2.4Ghz would not edit 1920x1080 until I replaced the video card with an Nvidia GeForece 8800GT 512MB one. Of the two pieces of software I've been working with, PD7 Ultra seems to be a bit less demanding of computer resources.
I consider the quad core I have now as just barely adequate for the HF100's files but I need to find out from Dell what the fastest quad core processor I can put on my current mother board would be. I sure wish what I have was a lot lot faster.
So that's where I come from when I say I'd go for the very fastest I could make myself afford.
I guess at 70 I'm just a kid to you...Hope my info is useful to you.