Hello Nigel !
My G5 Deluxe does have the Royal Enfield megaphone after market exhaust. I run regular unleaded gas, not premium, as my dealer said it wasn't necessary because of the computers' ability to adjust the timing. With the exhaust upgrade ( great sound ! ) and the 18 tooth sprocket, I am extremely happy with the performance of my bike. I live in California ( San Francisco Bay Area ), U.S.A. There is every kind of road you could wish for, from the coast to the mountains, to the freeways !! My Royal Enfield is quite happy on all of them !