With slot car motors what matters is the power and that is calculated using RPM and torque measurements and expressed in watts. If two motors had the same RPM rating one of them would have more power if it had more torque. For motors of the same make and model you can expect that motors with the same measured RPMs would also have about the same power. The Piranha and Gator black stripe replacement motors have different watt ratings.
I have tested quite a few motors recently and found that they have much more consistent performance than they did a few yeas ago, that is both good and bad news. For people that were willing to buy a lot of motors and race the best ones that is bad news. For people that do not want to cherry pick motors it is good news.
You can find test results for many motors listed here:
http://slotcarnews.blogspot.com/2007/02 ... -list.htmlThe Motor List is a little out of date, the person that did much of the testing has moved on to other things. I do have the list as an Excel spreadsheet, which is nice because it can be sorted to get the results for the same type of motor all together.