Any reason why your not considering the RB WS7II?? That is what I have in my MBX5 with an OS-2050 pipe and I love the combo. I race on a pretty tight track, not really meant for 8th scales and have plenty of bottom end. When I've gone to bigger tracks, with longer straights, I have plenty of top end as well. I'm on my 8th gallon through the engine and have had zero problems. I'm probably going to get another one to start breaking in to have as a back up. Just a thought.