Sample sizes are very important when considering a good ROI%.
I think the very best MTT players playing $1-$11 games can probably hit close to 100% ROI% over a decent sample. This depends on a lot of stakes though, I mean...if someone was grinding $1.00 MTT games can EASILY get 150% roi for example. I'm by no means anywhere close to being a "good" reg, however if I stuck just grinding $1.00 games I'd be very disappointed if I couldn't maintain a 100% ROI%.
I have a "long term" 64% ROI according to SS over 5600 MTT games ranging from $1-$11 games, primarily pokerstars
tournaments but even 5600 games isn't accurate enough imo especially in big field tournaments to know if it's close to what my true roi% is. I could very well have a worse roi% or better roi%. I wouldn't be interested is knowing unless I had 10k+ games to maybe read something into it. This is the first time I've actually ever filtered my MTT results by stakes. I'd imagine, for obvious reasons that I'm going to have a higher ROI% like anyone else in the lower games than say playing $11 consistently. Most of the better regs though are unlikely to stick around at the very bottom grinding $1.00 MTT's forever so a true roi sample size for these games is going to difficult to find. Most grinders stick around the $11-$27, because they are the level that whilst are getting tougher also have a good fish>reg ratio and most importantly is a level where people can start grinding for a living. The games are also still very beatable and can turn over some good roi numbers so I think you should look at trying to find out what someones average ROI% is in the low stake/mid stake MTT's are and then you can get an average as to what a roi% would be the lower you move down.
As for SNG's, it really does depend on which format you're on about. Obviously the more tables in each SNG , the higher the ROI% and there is a big difference between say a $1 SnG as opposed to a $11. Someone grinding out a 50% roi% in 180 man SnG's at $2.50 long term isn't likely to beat an $8.00 game at the same roi% long term (unless of course this person is improving and working on their game)