I usually am pretty adamant about sitting guys for a game or two once they dip to 99 in fatigue and try to keep everyone at 100.  Does anyone have any data on when (and how low) fatigue may actually start to affect play?

Can a guy still perform just as well as long as he stays 90+? 80+?  Where is the "cutoff", if there is one, and is this the same cutoff that starts to increase the chances of injury as well?

There really isn't enough data to determine if production drops off.    After all, it probably takes 2/3 of a season to get a 65 DUR guy to 90%.   But, and this is also very limited data, I've noticed most of my minor league injuries(I only check minor league fatigue for PP once a week) are at 97% or below. 

I'm with you ranger, I sit my guys when they get to 99%, except for the last 3 or 4 games of the season situations where I'm in a playoff hunt. 

It just gets me thinking, "what am I really getting for a player?".  I have several mega studs that sit at about 70-80 in durability.  This means if kept at 100% I am getting (just a quick guess, don't go all math on me) about 130ish 100% games out of them during the course of a season.

So for 30 games or so I have a utility guy in their spot of the lineup and in the field.  If I smear both players stat lines into one another, the conglomerate may look something like this (using rudimentary easy to follow stats):
Mega Stud: .320 AVG, 25 HR, 100 RBI (over 130 games)
Utility Guy: .275 AVG, 4 HR, 18 RBI  (over 32 games)

For all intents and purposes, I have, say, a position player with a season stat line of something on the order of .305 AVG, 29 HR, 118 RBI.  Not bad, but I'm thinking I may be able to fill that with a slightly less mega stud at a lower price with a higher durabilty, using one guy to get the same result.

One benefit of this is, once you make the postseason, providing you kept your guy at 100%, you now have a mega stud rolling in a short series, which makes your team better for that series. I can handle one or two guys like this on a team of mine....but I'm thinking in some cases it may be better to put more emphasis on durability to keep one guy on the field.

Or you can push said lower DUR guy, get those 550 AB's, and have him hover in the 85+ range in fatigue later in the year.  I just don't know if you want to hit the postseason with a guy at lower than 100%.

I'll try not to play a guy at less than 98% for most of the season.  But if I'm fighting for a playoff spot in the second half of the season, all bets are off and I'll push my guys as hard as needed.  No set time for when that starts, could be anywhere from the All-Star break to maybe 20-25 games left in the season.  More of a gut feeling.

I have no real data on where production drops off, or when injury risk starts to increase.  Word of mouth from some owners in previous forum threads suggests low 90's for performance drop off, but like Mike previously mentioned, there are no hard numbers to back that up.

ranger,

I like to have a couple of very durable guys in my lineup (155-162 games).  It makes things more flexable and easier, I think.  I've had thisguy for a couple of years.  Plays everyday (well, he had a pesky DL stint last year and missed 13 games), plays COF and 3B (GG in RF this year, not a great 3B) so I can rest my 3B when needed.

Career numbers are .790 OPS.  A bit less for me.  He's getting expensive and I think I'll let him go.  But guys with high Durability numbers are worth having. 

I also like to platoon a position.  Those type of guys usually come fairly cheap. 

Rest also factors in.  Agressive use of a rest backup in uncompetitive games can be worth a bunch of games.  I have a 1B with 82 Dur.  Not using a rest backup regularly, he's given me 150ish games.  Using a rest backup for him in all uncompetitive games last year, he went 162 at 100%.