I felt an increase in power from 3000rpm and up with the spr's....they have great midrange torque...ask anyone on here that has themWhat kind of driving is the car going to see and where do you want to see gains? Stage I's tend to boost the power band in the lower and middle parts of the RPM range, while stage II's tend to be more focused in peak gains in the upper RPM range. I went with stage I's because my car sees 2500 - 5000 RPM's all the time, all day. I do see 6500 rpms a lot but in the grand scheme of things it could be considered rare. So I wanted a set I could feel all of the time not just above 4800. It's a personal choice of driving style and habit that will help you make your choice there. Stage II & III's can be a bit rough driving it as a DD, especially those cams with a bunch of overlap. Rough idle and loss of manifold vacuum can be tough with a stick in bumper to bumper traffic.