I am building a TEF table in the guide in the first post, this is how far I have come so far:
Click image for larger version.  Name: 20 TEF.png  Views: 286  Size: 55.9 KB  ID: 71965

I think its a bit interesting that a 18 y/o Fast-trainer as a 7 star has the same TEF as a 20 y/o Fast-trainer. I expected the TEF to drop more with age, but it seems to stay the same until at least 21 y/o. But I will check this next season. Maybe it even stays the same until 22 y/o?

Do anyone have any questions on the TEF table? The first TEF number, like 0.28 for an 18 y/o 4 star fast trainer, is cleared from any impact of training levels. IE, its the TEF this kid would get if you only used level 1 drills. Then on the same drill I have just adjusted that number for Lvl 2/3/4 drills. Then follows the result of the TEF when adding a Special Ability (50 points) or New Position, I have based this number on having lvl 4 drills. They are easily adjustable. The formula is ((50*4)/TEF)/15. The last column is the cost in Rests to add 20%, to go from in this example 4 stars and 60% to 5 stars and 80%. This formula is also based on lvl 4 drills and can be adjusted in accordance with this ((20*15)/TEF)/15.

I have sent out my spreadsheet to a few people, if anyone have done any crunching themselves, they are welcome to chip in with some numbers to this table! (and as I have said before, if anyone want to get a copy of the excel-sheet I am using, drop me a note and I will mail it to you!)