question for people with DSE minitubs

[ArisESQ]

I currently have a set of wheels which are 18x10 with 5.75 inch b.s., and will be minitubbing my car shortly. I plan on having the wheels widened to accomodate a larger tire, and to fill in the new wheel well.

my question is, assuming that my wheel is currently 10 inches wide with 5.75 inches b.s., how much can I widen the rims? Is 2.5 inches sufficient? I would rather not get into changing lips and such to modify the offset, since I am very satisfied with how the wheels already look. I just want to fit a larger tire. Any feedback will be greatly appreciated.

Thanks!