Bob,
I use a few electric motors and I am still pretty well confused most of the time as most manufactures have there own numbering systems.
You will here about speed 400's , 550's , 600's in can motors.. I use a few AXI brushless and they have all kinds of numbers on them..These are direct drive..I have 2 MPI brushless with gearbox that work fairly well. it's a 4025 with 6:1 gearing. All useing 3 cell lipoly batterys.
When I buy an AXI motor I call Hobby Lobby and ask what size do I need. They just sorta sell them for weight of model. Go to there web sites Bob and you can get more confused.. Good luck.

Jim