If you don't think you want to bulk up and fight at heavyweight, I can understand staying at 205. You'll have a reach advantage and as long as you know how to use it you should be fine.
Fighters come in all shapes and sizes. The generic 205 fighter, who stands 6'2 and is relatively thick, is just a common build because it works for alot of styles, whether it's a wrestler, a brawler or a submission fighter. Still, with longer limbs there are lots of advantages that you'd have.
The first thing I suggest working on is range control. Learn to keep your opponent at range with your jab and leg kicks. Also work on solid combinations at distance and using high kicks, because that will something that is very useful, given the range that you'd get out of them.
Also, work on your clinch game. If an opponent gets inside on you, it will be important to know how to control the inside. The best way for you to do that will be to control his head with your arms, as they are useless if you are going to try and fire short, wimpy hooks and uppercuts. With the length of your legs, using knees in the Thai clinch will be a great way to beat an opponent or convince him that getting inside on you isn't a great idea, while doing good damage to his body and face.
Also, work on fighting off of your back. If I were you, I'd watch tapes of Brad Imes last two fights, which show some really knowledge of using the gogoplata from the rubber guard (a great submission for tall guys) as well as watch videos of Kendall Grove and the other guys who are regularly taller than their opponents.
The real secret for a tall guy is learning to go beyond the closed guard off of your back. Make sure that you can effectively use a spide and, ideally, rubber guard, which will allow you to use your long legs in the most effective manner. Also practice using a good groundnpound attack against an opponent chasing armbars, which will be your biggest problem if you get on top. Learn to keep your elbows out of the submission and move them around quickly to prevent getting put in that situation.
Best of luck.
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