Let me put it this way: if you balk at the price of renting a 5D2 for a few days, then your finances aren't yet solid enough to warrant buying the 5D2 without having specific, articulable reasons for doing so.
Right now, you're merely uncertain as to whether or not you will benefit from it. Full frame calls to you with a siren song. It does that to many. But unless you know specifically how you will benefit from it, it's just a siren song.
I'd at least wait until you can afford to rent one for a few days. That will tell you all you need to know. But realize that you'll need more than just the body -- you'll need additional lenses. The financial commitment will be considerable. The 35L and 85 are unlikely to be sufficient for your needs (you will know if they are by examining the focal lengths you tend to use with your 7D. If they are clustered around 50mm and 135mm, then the 35L and 85 might be enough. If they're spread out, or if they cluster around significantly different focal lengths than those, then you'll need additional glass for sure).
Here's the thing: shooting with your 17-55 IS on your 7D will be much like shooting a 5D2 with a 24-105 f/4L (a combination that many rave about). Yes, the 24-105 will get you slightly wider and narrower angles of view than the 17-55 on your 7D does, but not by incredibly huge amounts. The resulting depth of field will basically be the same. The noise may or may not be the same, depending on whether you're already wide open and shutter-speed limited. In high ISO conditions, you are aperture and shutter speed limited (which is why you're shooting at a higher ISO to begin with), and that will put your 7D and 17-55 IS on an equal footing with a 5D2 with the 24-105L in terms of both depth of field and noise.
This is why you really should have solid, articulable reasons for switching to full frame when your finances aren't solid enough to make it possible to switch painlessly (either by renting for long enough to determine whether it's the right course of action, or by buying the 5D2 while you retain possession of the 7D). The two are closer than you might think.