to me, lvl 5 trainer is the absoluut minimum if you want to train your players in a good way.
and i think that the difference between a lvl 5 and a lvl 6 trainer is about 2.5 weeks of extra training. between a lvl 4 (advanced) and a lvl 5, you'll have 3, maybe even 4 weeks of difference...
the difference is rahter large between a 4 ( advanced) and a 5 ( superior). and their still is a difference between a lvl 5 and 6 (significant enough to make you pay the extra 500k to get that lvl 6 trainer)
for the lvl 7 trainer, i got no data on that, so can't help you their...
also, i'd put your lvl of your trainer in fucntion of which position you want to train.
if you train monopost C position of C's all the time, a lvl 4 could do the job.
however, don't try training an SF with a lvl 4 trainer, or you'll never get him to a decent lvl... even with a lvl 5, it's really hard to get him up to a decent lvl... for SF training, i'd suggest a lvl 6, because their so hard to train well...
on a side note, got 2 from teh 5 feedback for my manual. expect to see a post somewhere towards the end of this week, to announce the new manual
Rev