Of the two, the 7D is a more versatile, multi-purpose camera. I use a pair for sports/action, wildlife, anywhere I need a telephoto's reach.
The 5DII is my choice for portraits, landscape, architecture... and low light. It's image noise handling is good to about one stop higher ISO than 7D, in my opinion. Canon rates them the same, but in my experience the 5DII's AF, even though it slows down, also continues to work about one EV lower light than 7D's. My comparison maybe be skewed, though, since I use the 7Ds mostly in AI Servo and the 5DII mostly in One Shot. Tracking moving subjects in AI Servo with 5DII is largely limited to the center point alone (though there are six hidden AF Assist points clustered right around the center, that can be enabled, but only work in AI Servo).
Yes there's a bit of a bump up in image quality and high ISO handling with 5DII.... It captures gobs of fine detail that allows big prints and/or lots of cropping... at the cost of slower, lower performance AF system, and loss of a lot of the nice little features on the 7D, such as the assignable buttons (and the 100% viewfinder, frame rate, active matrix focus screen, wireless flash control and more). The 5DII also uses an older design 35 zone metering system, compared to 63 zone iFCL on the 7D. In use there''s some differences, but not really a lot.
Frankly, crop cameras such as the 7D and all the 18MP models are pretty darned good. The 5DII may have 2.5X larger sensor, but the pixel density of the 7D is more than twice that of the 5DII. In the end, if you'll need to make prints larger than, say, 13x19" before you'll start to see some of the difference in the fine details. And with good post processing, the differences will be minor until you get to a much larger print.
I like using the two formats together, each for what they do best. I suspect that even if I upgraded to the 5DIII and it's much better AF system, capable of sports/action shooting along with everything else, I'd still keep using the 7Ds for sports/action for their "extra reach" (yeah, I know it's "not real", but the 7D really does "put more pixels on target").
Flash sync with 7D is 1/250... with 5DII it's 1/200. With studio strobes it varies a bit depending upon the lighting gear, but the 7D syncs fine with my Norman monolights at 1/160 and my 5DII does fine at 1/125, though Canon recommends 1/30 to 1/60 with both cameras.
Oh, and the 7D has a quieter shutter than 5DII. I found that out doing equestrian photography. I rarely see a horse react to the 7Ds shutter sound, but have spooked a few with the 5DII.
Welcome to POTN... Beware, though, there's a lot of GAS (Gear Acquisition Syndrome) around here and it's highly contagious. 