ROI =return on investment.It is a term use in MTT's and SNG tourny's.
I believe a good player should have no problem keeping a 30-40bb/100 average.
1st)Live players are teri bad in general.They are way to lose,to drunk,to passive,have no idea about odds
2nd)A reason a good player can keep that good of a win rate is opening raises.At any given live table you can find people opening UTG for 4x-10x the blinds,and getting 4-6 callers.Compare to online this will never happen.
So if your good enough you win 40bb/100.Thats $80 for ~3hrs playing.So to make 8k that would be 300hrs.300(hours)/25(days)=12hrs a day.That is with no down swing no tilt,tiredness,not counting tips,and presuming your good enough to win at that rate to begin with.