Upgrading

Looking to go from a 30D to either a 7D or a 5D Mark II. First of all, I can't afford L lenses, and I enjoy the "extra" length of my lenses using a crop sensor.

However, I like the IQ of the 5D and I'm wondering what the trade offs I'm going to have to make. I'm not a professional and have been lucky enough to get some very good images with my 30D, (which I bought when they came out).

I'm leaning towards the 5D, but my daughter owns a 7D and it is a great camera. 
I'm just wondering if the differences are great enough for the added expense of a 5D over a well outfitted 7D. I don't do action photography, but I do a lot of low light "club" like photography.  Does the high ISO in the 5D negate the loss of a infrequently used, but happy it's there, camera mounted fill flash?

Just how bad is the AF on the 5D II? Does it really suck in low light?

Anyfeedback would be appreciated.

Thanks!

John