If your receiving the signal back to shore on a live feed then going way over 300 is not a bad idea to have or look into, since you don't need to see where the boat is, as long as you can see where your going, but i would ask why anyone would go that far out with a boat even if the lake/river is that big, what if it cuts out, you loose the feed?
I can understand why people who fly model aircraft do it, they have a real need for that distance, but a model boat? our lakes about 2 acres maybe a bit more (never been out to measurer it)
After going out half way you can't see if unless its a yacht even then its hard to tell which way your facing sometimes.
I suppose it comes down to cost, no reason why if you can afford it why you should attempt to do things (That's called progression and being an innovator) but i do wonder why you would spend serious amounts of cash for that feature with no real need for it?
Hey but if it makes you happy and you enjoy it then that's what matters rather then what some think, don't let me put you off, but at least be aware of the risks i pointed out should something fail, at least that way you can make a strategy for recovery!