Good 79T suddenly appear now. should i buy him?

[Toxcatl]

let say, i divide the VALUE/WAGE = got more than 50, is he fast trainer? is there any specific value to differentiate it?

I don't know. That's the problem. This coefficient depends on your level (well, strictly speaking, it depends on OQ of the player). You can compare, let's say, 18 y/o players to each other while deciding whom to buy if their Overall quality (OQ) is more or less the same. But you can't compare players from different levels (read: with significantly different OQ) or different age.

A piece of theory. Value of a player depends on his Age, OQ, Talent (hidden) and who knows what else. Wage depends on OQ only. Special abilities and Positions have no effect on both these parameters. If we agree to compare only 18 y/o players, we are getting rid of Age. By dividing Value by Wage we reduce the influence of OQ. Btw, that means you can divide Value directly by OQ instead of dividing it by Wage, but first you need to calculate OQ's exact value by the formula: OQ = Qp/4 + 5*(Lvl - 1), where Qp is percentage quality, Lvl is your current level. You can use this instead, AFAIK Nik uses it. It's probably even better; I don't want to explain here why -- this reply is long enough.

The higher OQ, the lower this coefficient (V/W or V/OQ), and difference between slow-trainers and fast-trainers becomes less and less noticeable. On high levels, like 25+ or maybe higher, there is no difference, and it's impossible to separate them. All the players of same quality have same Value!
Graph would look like this:

(pardon my mad paintbrush skills)
The red line is AverageV/W(OQ). Being above it means the player learns fast, below it -- slow.
I tried to get AverageTalent(OQ), not AverageV/W(OQ), but I failed. Need more data and mathematics than I have =]

I don't have enough motivation to start with 1st level team, play just enough to get promoted, and gather data from all 18 y/o players I could find. But with this we would know what value of Value/Wage (or Value/OQ, or just Value) is good for every point of OQ for 18 y/o players. Not as elegant solution as finding the formula for Talent, but it would serve. I had statistics for levels 7-9, but I lost it.