Back in the old days of 2003 I raced a predator with my stock speed with the toaster exhaust. It was almost a dead even match up with the Speed just barely able to crawl away from the predator on top speed . I dont know what mods you have or how much more advanced the predators have become but I seriously doubt the margins have changed all that much. If you practice your holeshots you should do fine.
Did the PRED have a stock exhaust?
I only ran the stock exhaust on my Speed for a short time, then switched to HMF. I switched between the stock can and HMF can quite a few times. Even with the stock can on my Speed I haven't had any problems with other quads that were still running stock exhaust.
I don't believe the HMF pipe could make much differance with the stock can