We had a guy that was 2320 on line in blitz 2 years ago and came to the chess club believing that he will need 6 months to get NM and then he would try for FM and IM.
In his first tournament he couldn't beat 1000 rated players , his second was better and his 3rd dissapointing. 6 months later he abandoned his ambitious project and we never saw him again.His last rating was 1375.
Another guy came with on line rating around 1800 and he is now at 2000 OTB but he too had a lot of trouble adjusting. His first tournaments were disheartening but he was stubborn and eventually did it.
It's impossible to find correlation between on line and OTB , they are 2 very different numbers gained with very different way(different opponents , different conditions of play).
Yeah I know that I likely wouldn't be 2200 OTB but I think that with enough time to adjust I could reach at least 2000. It's not like my chess understanding is immediately going to disappear if I start playing OTB.
OTB chess is not about understanding only. It's many many more things. If you haven't learned to stay focused for 4 to 6 hours , adapting is not going to be easy.Add to this that you often have to play 2 games a day , or 3-4 games in a weekend and you will realise that there many more non chess related skills that decide the result.
But it also depends where you will play.Since rating is actually a number that depends on your opponent's skills it's easier to be 2000 in some places than it is in others. If you played in India or Russia I would tell you that you would probably never be 2000 maybe not even close.
Some good points. I'm pretty good at staying focused for long periods of time but I would definitely need to work on other things like OTB visualization and calculation (I'm so used to looking at a screen). There's also just the fact that I would be out of my comfort zone. Playing someone face to face is different than playing someone online from the comfort of my home.
Remember that on line you play someone that might do many things at the same time. Small things capable though break concentration(answer a phone call or a door bell).In OTB you play against a guy that will do nothing else except playing chess and trying to beat you. Some of your opponents might prepare for this tournament 6 months or more and they want to prove something to themselves.There are certainly many differences between on line chess and OTB chess. I don't doubt that you can adapt but you will need a lot of patience and determination to get over some bad results against some 1000-1200 rated players.On line players usually give up after losing against 1000 rated Chinese kids over and over again(I use "Chinese" because they are the nemesis of a friend , it might be any kid).
Chess has become increasingly difficult for those that haven't start it as kids.
Yes I realize that many players don't take online games very seriously and are much stronger when you play them OTB, especially titled players. For example I played GM @DJ_Haubi in 4 daily games (2 standard, 2 chess 960). I won 2 and drew 2 which sounds impressive until you realize that he was playing like it was rapid or even blitz while I was taking a really long time on my moves. So he was basically playing with a severe time handicap and still giving me a hard time. Some of his moves I didn't see coming at all. I know that I wouldn't stand a chance against him in a serious OTB tournament game. Most of my 2100+ daily opponents do take their games very seriously though. I often play against these guys for months because we are both taking our time on every single move. They have a fierce determination to win, or at the very least to not lose.
And yet, whenever I play you, I am lost within 10 moves (compared to playing Stockfish which I am only lost at around move 20-25).
Just bad luck I guess. Also most of our games were played a while back. You've gotten much better since then so you now have a much higher chance of holding your own or even beating me. 
(at least nothing like what we have access to these days).
I'm above 1700 in blitz/bullet/daily/rapid on this site, and only played my first OTB tournament just 1 month ago... I lost multiple games to kids as low as 1100 rating there and as young as 10 years old.
OTB tournaments are just another beast imo.