Yes it is confusing isnt it! I actually find that the various numbers used are often quite useless anyway.
What I want to know as minimum is the Kv, the maximum current, and maximum wattage. With this I generally decide what will do the job. The old designation of "400" referred to older brushed can motors - and as for paying £60 for one with an ESC, that seems ridiculous - and yet again proves that "brushes are for floors". A cheapy equivalent speed 400 motor in brushless flavour can be had including a speed controller for peanuts these days.
There are just so mnay types of motors available these days with different winds and so on, that a "backward" comparison chart would be nigh on impossible - trying to find a one size fits all type motor is just not practical, because different model types require different power types IE high revs small props and low revs large props,each respective motor may well be 100watts capable for instance..... but produce that power in a totally different way.
No need to stop trying to understand it all, just accept that you will never know it all ( none of us do ) ut the basics as often mentioned hould get you on the right track.
1) 100 watts per lb average for typical sport model.
2) fast model - high rpm ( high Kv ) small diameter large pitch prop, probably inrunner
3) EDF - high Kv, very high revs.....almost always inrunner
4) slower model - the opposite....usually outrunner.
denotes 
) but I'm finding it very difficult to understand the variety of ways that are used to describe motors. Its almost as if the manufacturers think it should be kept a closely guarded secret unless you're already in the know.
