Most of my team are "fast trainers". I spent the 500 green packs that I had saved today. It took me from 104-111% - 1.8points on my first team average (3 million pound improvement on my newest MC). Though I was disappointed with my goalkeepers improvements, the rest earned between 6 and 10% - mostly 8-9 cept for a couple of my older perfomers.

So, it may be worth saving your green packs over the season, to see how many you can get. I think I'll end up with a lot less this season, even though, because I am up against stronger teams than me in all competitions (knocked out of the cup by one right off the bat).