widest tire w/minitub, w/out moving springs?

[joflaig]

I have the widest tires on the rear possible now with the stock configuration, but I like the look of even wider rear tires, maybe 2 or 3" more. I don't have any qualms about modding my car, but I do get conflicted when it comes to chopping into the metal and replacing things...but anyway, what's the widest you can go without having to move the springs? Anyone done a mini-tub here? Any pitfalls for a street car, I'm not thinking of?