^^
It might be my eyes but judging by the ISO test between the 50D 7D and 5DmkII, I'd say the 50D out performs the 7D...
In practical application, I've noticed having to deal with more color noise with the 50D files and more luminance noise with the 7D, which I think those charts lend themselves to (the 50D images almost become 'warmer' as the ISO gets higher). When it comes to print, though, any differences become highly negligible, honestly, and add in some decent noise-attenuating program (I use noiseware pro, personally), and both can generate usable images up to 3200 and I'm about 50/50 with getting good stuff at 6400 with the 7D.
To the OP:
You'd probably be best of initially investing in a good NR program (there are many). It's way cheaper than dropping 17 bones on a new body for an incremental upgrade in the processor (they both use DIGIC IV processors, the 7D has 2 but that only really buys you speed). You're setting yourself up for disappointment (though you'll not be disappointed by any of the other features, I can assure you).
Unless you're shooting in a lot of low light, the 7D won't buy you terribly much in terms of IQ. It's way cleaner up to 800 and you have the option to adjust your ISO in 3rds of stops (or half stops, I believe) but it, but 1600+ you're probably going to have to deal with (or accept) the noise in some form.
I only upload web-res files to my flickr account so these don't lend themselves to pixel-peeping, but these are all shot with the 7D,some as high as 3200ISO:
Flickr: ToddMcKimmey's Photostream