from my (admittedly limited) experience of clip ons & rear sets (that's one for you old ones, especially mickthelimey)
I would suggest any crotch racer type stance is OK if you want to just go like a bat out of heck all the time, butt hanging off the seat, but for around town it'd soon bring about a sore back, aching wrists & general discomfort.
like I said, my experience is limited, but that is what I reckon...