last time i checked every kill ive had using the M18 was a shoot n scoot maneuver. very few were rolling like you say. The M18 is better off ambushing and fast unseen maneuvering than what you say.
what you really wanna do is get in firing range and the flank. stop the Hellcat out of sight, take your shot. This improves the accuracy and usually one shot kills. Immediately displace and set up shop elsewhere. Dont go gunho into the fray shooting off rounds or the enemy will probably counter you fast enough to stop you no matter what theyre in.
That how I've got most of my kills in it. I drive up close in some trees or peaking over a hill and stop. After I shoot I'm back on the run. I have had several kills while I was at top speed. Most people still underestimate the speed it has and shoot behind you.
Any plane is a threat though and i think I've been turreted by planes more than I've been killed by tanks in it.
That being said its my ride now taking the place of my jeep