x-pipe and exit in front of rear tires?

people have said for many years if you are goign to run a flow master go with the next pipe size up. i dont know if they are really that bad, i have heard of guys gaining time by switching to a straight through muffler from a flowmaster. i guess it really depends. maybe if the size pipe you are using is already on the small side. the only flowmasters i ever used resonated like no tomorrow in my car, enough that i will probably never give them another chance. they do sound great on other peoples cars though. lol.