IMO, strength and (light) weight are more important than an impressive diameter.
Of course, the sculptural design of the wheel matters a lot as well.
So, I'd stick with 16" x 7" on an Integra.

Any bigger than that & the wheels look cartoonish IMO.

Physically, though, I'd bet you can manage 18" x 7", depending on offset and the amount of lowering. They've been fitting 18" s on Civics since the early nineties...so any decent wheel store can help you sort out the correct dimensions.