You are way, way off on your thoughts about competing. You say you have fairly big legs now, right. You could easily compete and do well, right now. If you would diet down to around 245 and come in shredded, you could easily win the supers at a state level show. It's all about being in shape, as the leanest guys usually win.
Another thing, you will most likely never be as big as you think you need to be in order to do well competing. Also, you will never ever think you have that look. You know what I mean, it's the bodybuilder look. As a tall guy, you will forever see yourself as the stringbean. I know I still do . As far as being competitive on a National level, well that's not going to happen. Unless you can get the size that Noah Steere had, there's no reason to even entertain the thought.
Lastly, I can tell you think the grass is greener on the other side. 99% of the guys on here would like to be taller. Hell, I'm 6'3 and wish I was 6'7. Maybe you should be more appreciative of what you do have and what you have accomplished.