The 35mm on your crop sensor is basically a standard lens. No magnification. On a full frame it is a medium wide angle lens. A 50mm on the full frame would give you a similar angle of view and the 35mm on your 7D. When I say similar I mean approximately, not exact.
The 5D would have better IQ especially in low light. Both are amazing tools in the hands of a good photographer. Rent one and see what you think but you may do better spending money on a lens or other gear to improve your tool kit.