Please see mods in sig. Wanting to add x-pipe with high flow cats. Thinking either UPR or Mac Prochamber. Both pipes advertise gain of approx. 20 plus rwhp. I know there is some bullshit advertising in there. But, what do you think real gains would be for this one mod? 10-15 rwhp? I am at 290 rwhp now w/ 4.10 gears and would like to see 300 plus to the tire. Thanks.