I'm estimating a 20% ROI player would probably have an ITM close to 40%, so OOTM of 60%.

Pr(OOTM 8 times of 8)=0.6^8=0.0168=1.68%

So basically if you divide the games you play into sets of 8 a player with a 40% ITM can EXPECT to finish OOTM in all 8 SNGs from the set about once every 60 sets, or 480 games.