I think once you go to fullbores you pretty much sealed the deal when it comes to an oversized tank.. I have never seen or herd of anyone hacking up fullbores for an ims or Clarke tank..
As far as a bigger tank on stock plastics, I do think that alot of times they look like shit.... Me personally did not think they would look good on my bike, but I was suppose to head back to glamis this past February and last year when we went, I couldn't ride. Every time we got to where we wanted to be, I was extremely low on fuel.. Even with my extra 2.5 gal can on my grab bar. There was one ride I didn't make it back... I desided that function was worth more then looks.. Turns out I love the way my bike looks with the big tank..