yeah, this is a tricky situation to judge. I, myself, definitely have a good running game with the occasional tough going. Against an average D, I get 100 yds with Jackson, and I expect to get 100 yds. I have been upping the cpu run blocking incrementally lately, but feel fairly comfortable with this rating. I originally had it set lower and played against the Vikings and Peterson only had 60-70 yds. As much as I enjoy winning, I was expecting to see him have a bigger game. I will say, however, that I keyed on him constantly and purposely set up tougher run stopping Defensive alignment to force them to make Ponder beat me. So, I feel the running game is close to being correct. The player tackling slider impacts this as well. The lower the player tackling, the more the RB not only breaks tackles, but he also reads holes and situations better to completely avoid being tackled at all, it's as if he 'feels' the defenders better and sooner and avoids them better. I also had a game where mjd simply ate me alive! I didn't key on him as much as I should have and he took off for like 150 yds or so. As far as the avg game against the avg back, I feel like this Run blocking setting allows for them to set the edge decently and get a decent push up field for up the middle runs. And, I also feel this setting does allow for the ratings of the offensive lineman to dictate what happens. Play against the 49ers if you don't believe me! lol. With these ratings (or something close to them as I've been tweaking them for a week or 2), SF's Oline pushed me ALL OVER THE PLACE!! Kap went off, Gore went off. I lost that game by 20, actually, and could not stop the run. Also, against the Packers, Clay Matthews was killing my run game, and I believe I ran for only 60 yds or so off 20 carries, so there's a case in point of struggling against a good D.
So, I guess, in conclusion, I'll say this. For me, right now, I believe these settings (player and cpu) allow me to run well and allow the cpu to run well, and they allow the cpu to run REALLY well if they have a good oline. So, it's fairly realistic, I believe, but is definitely tweakable. If you're purely simming, and not playing at all, I'm not sure, you may want player and cpu both set to the same number and for that, I'm not sure whether 20 would be good, or 27?