Well, Reloaded's speed is still being worked on so there really are no exact specs as yet. Suffice to say the faster the better. I can only add my specs and report how I have found things so far.
My specs.
Q6600 Quad core, the second better variant, I can't remember if it was an E, or B they added to the name
8 gig DDR2 ram (faster than most but again, without going into the bios can't remember it's exact speed.)
Geforce 260GTX (decent in it's day but showing signs of age these days.)
I get about 12fps on a reasonable scene using the last official update, with settings on full, knock em down and I can get 20+ fps.
However, I am privileged to have been lucky enough to get a interim version. Please don't start a flame war about this, people are given test access occasionally, it's all for the benefit of FPSC. I have no idea why I was contacted for this, apart from that I am active on Lee's blogs, these forums and also do many FPSC videos. Plus I have had a game published by TGC in the past, and so, have spoke with them before. Still, I feel lucky and honored to test the software and provide feedback, helping cement the next update for everyone.
With this version, I get something like 40 fps on full, obviously dependant on the scene. Once I have played with the settings I have achieved over 170 fps (not looking at the sky I might add), with 70 being the norm for more detailed parts. Obviously it is still choppy at times, but it is beta and will be improved. I am expecting big things for 1.04.
So if you have a machine near my spec I think you will be okay, although obviously if you are actually buying a machine for this then get the fastest video card you can, plenty of memory, and a decent cpu, in that order.
Any Geforce card with the 60 (460,560,660)prefix is going to be pretty good in the main. Obviously the 80 ones will be better and so on

Any 50 or less ones are not as capable, and I would avoid em if you can, even go for an older 60 card than a newer 50 in my opinion. Although a 650 is probably okay..ish.
Anyway that's my opinion. I used to build PC's as part of my job, so am fairly well versed in building gaming PC specs.