I personally run the N528XR and it is a very fast engine when you port it correctly. I changed out the 9mm insert for the 7.5 and it is still an animal with about 10 minutes of run time. I raced this past weekend against several bigger motors, one of them being the new OS 28XZ and he had that OS rung out as far as it would take him and he had nothing on my 528 out of the corners. I'm not sure if it was modded or not but he gave me some good props afterwards about how he leaned his motor out to the point of being too lean to try to hang with my truck. I modded one of those 28XZ motors for a guy in Chicago and he has reported back with very good results so I imagine a modded 528 vs. a similarly modded 28XZ would be a pretty close match up on the track. Both motors have a good base design with plenty of improvement room to be made and I can also mod either engine to full race spec for $80 usd which is very respectable for the amount of work they require.