I have been using Isky only for flat tappet stuff, as they won't stock the austempered cores I need for roller cams. Isky is far superior IMO in both fit/finish and lifters...power is as good or better than anything else and I've yet to have any problems with their stuff...also run their solid roller cams and lifters is higher end builds with excellent success. I will say though, 300HP can be made with Comp's 275DEH cam.