i am 190cm there abouts.
i have ridden 20" 19" 18" and beleive it or not 14" (it was a mates slalom bike just for fun )
i would suggest 19 or 20, perhaps 20 preferably.
GT's have really short top tubes. at the end of the day...thats the more critical dimension than a seat tube.
The other problem...with the 19 they tend to have tiny head tubes. ie the same as a 18. what this means, is that if you ride a decent amount of seatpost (and if you are 6' 2" that is likely), then the drop to the bars is large. in turn, this means sore neck...from trying to look up the trail.
Sure, you could run lots of spacers and steep stems and risers bars....but man....that is just not a nice look. In fact you see it on lots of GT's...where folks clearly find the front end way too low.
Solution.....20" frame. by comparison, they have gigantic head tubes , which puts the stem and a good height, and you can run a nice decent length 0 degree and flat bars and still be really comfortable.
The links below in my sig describe this a little. The 95 is a 19 and perhaps slightly too small for me really. it had a fair bit of seatpost hanging out, and had quite a lot of drop to the bars.
The 94 is ideal. imho anyhow. Not huge amounts of post hanging out, a 140 0 degree stem minimal spacers and moderate drop from saddle to bars. This bike feels really good to ride.
The 92 is the same frame size, however the stem is a little less ideal, and long term, i also want a 0 degree 140 cattleprod for it (anyone? anyone?). the stem on it is a 150 flip flip, however when flipped its actually closer to 155... too long! and also dumped too much. However when it is in its upright position, equally it puts the bars way too high, and makes it hard to climb steep hills.
Oh well, I guess I'm just going to have to build it up and see how it fits. Fortunately I do have a couple of longer stems and a riser bar in the parts box that I can use to stretch it out and lift it up if need be. I hope it fits - wife will kill me if I bought something that doesn't fit.
Cheap, light and strong. Pick two.
1992 GT Edge; 1996 GT Zaskar; 2000 Rocky Mountain Hammer Race;
2012 Norco CCX monster cross custom build