I also have a converted GTX with a bulkhead and thigh straps. Seat height is 6 inches.
The GTX (8.1) is designed for the larger paddler in the 180-220 pound range according to the Dagger web site. THe Volume is more like 78 gallons which makes it more than the creek boats. However, one on the down side to the GTX is that it is hard to roll according to what I have heard from some kayakers. Originally it was marketed as a easy river runner with some play potential. I think Dagger thought it was going to be easy to roll too. If you think about it, with all those angles on the sides and the flat bottom, it is not surprising.
With your weight and size you should not have the stability issues that I have had in bigger water where the waves mess with the deck.
Assuming you're not slipping out of position, you might need to slow the roll down a little, at least at first. You are light for the boat- but that should impact your ability to play for moves other than surfing- I can't imagine you would be doing too many other types of moves other than surfing in a GTX anyway, because of the volume- I assume this is your river runner/creeker. I would try it more before looking at a smaller boat.
Bill
Guess I read in the posts what I was afraid of - that it is a hard boat to roll
I was hoping it was me, instead of the boat. Lately my roll even in the open boat has not been the best.
I will go to the lake and really work on it. I LOVE the way it handles when I'm upright .
It is only for the bigger water, like the ocoee, that I got it for. I have others that are for playboating (XXX) and just fun (Perception Blaze 6.9).....
Right now I can roll it with great difficulty,..and occasionally I will hit a roll that is done right and it feels good.
My concern is; will I be able to learn it well enough to roll if needed on the Ocoee???
I will really try the next several weeks and see where I stand then (in fact I have put my kayaks up for a while, until I get my canoe/C1 roll back in good form - I think the kayak kinda screwed my openboat rolls up ).....
I think that the boat is a good idea boat for most all river running so I think that it is worth the effort that you are putting into learning to paddle it well.
I have used it on creeks and river like the Tellico and had a great time. It seems the larger volume rivers like the Ocoee and Pigeion over 7.5 feet will want to play aorund with it more than I like. However, your size should have you trimmed out and bobbing niceily on top of the water.
My son tells me that my roll looks very deliberate and in two parts, the roll out then the low brace. The reason probably has to do with wanting to make sure that I am in the right position before I proceed since there is some difficulty with the boat. However, the roll really should be more fluid and one motion. THe other issue is that most of us try to roll too fast and to soon. Practice counting to five or ten in still water before trying to roll. Next time you are in moving water, try waiting. Having said this, it is still going to be a challange trying to roll if you are half way through Table Saw or Humongus. Therefore, just don't filp. I also think that your playing some in the boat will help your balance and rolling.
Notice the ways of slalom paddlers and the way they stay over their behinds and knees. This has helped me not to paddle favoring my on side so much.
If you think about it, with all those angles on the sides and the flat bottom, it is not surprising. 
where the waves mess with the deck.
. 
