performance of running win 7 vm on imac

I am looking at purchasing an Imac (2011 21.5-inch: 2.7GHz). I have an aging windows 7 machine that I want to replace. However, I have tons of software and settings that I would like to keep as is. I'm would like to convert my win 7 pc into a VM. If I do this and run it inside of virtualbox or vmware on a new imac, what is the performance going to be like? Will it slow the imac down to a crawl? Im pretty sure it would choke my unibody macbook to death if I tried the same thing on it.

It will be very spritely.

Unless you run a lot of games, which really need to full bootcamp boot into windows

It's nothing like running emulation, but take a look at the current Mac update bundle as you can get VMWare fusion as well as other use ful apps for $49

MacUpdate Spring 2012 Bundle - 11 Apps for only $49.99

no games. The main things are windows media center, plex server, log me in, splashtop, playon. Thats really about it. Everything else is extremely light use. I can even run some of those on my imac instead.