How much difference would a high quality road bike make?

I'm sorry for such long text but if you could please read the whole thing and help me out, I would greatly appreciate it. I've been road cycling for about two months and am currently riding and old 2004 Giant DCR2 (hand me down). It's a road bike, but its this weird endurance touring bike or... show more I'm sorry for such long text but if you could please read the whole thing and help me out, I would greatly appreciate it. I've been road cycling for about two months and am currently riding and old 2004 Giant DCR2 (hand me down). It's a road bike, but its this weird endurance touring bike or something. I just recently road a 30 mile ride in 1:37:05. That's an average speed of 18.7 mph. If I had a high end, carbon, bike, how much would my times improve? Would it even be noticeable? I really want to get better and train harder, but I'm stuck on this bike. Also, I'm 6'4" and still growing. I did a size calculator and it said I need a 62cm bike. What good bikes could you recommend to me that come in such a size? Excuse me if I sound like such a newbie; I don't know much about the sport. Thank you.
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