...or should I keep building miles on my Hybrid, that is the question?

I currently ride an older Trek 720 hybrid. The bike is in real great shape and has been tweeked a bit to suit my riding style which is mainly road useage (zero angle long stem and 700x25 tires). It has a flat bar.

Right now I'm riding three times a week going 13-20 miles at a pop at an average speed of 15mph (not counting any commuting miles). On the weekends I've been throwing in some 30 mile rides, which I wish could be longer but are not due to my speed and lack of time. I really enjoy going fast but I'll be darned if once I get to 16-17 MPH it becomes an absolute bear to keep that pace, but 14-15 I can do all day. I assume my pseudo upright position is at fault (not including my physical limits).

What bothers me most is at 20MPH I feel much more confident on the roads I ride (35 mph) in dealing with traffic and other "roadies", but I can only keep that pace for about five miles.

Would a "road bike" make me faster, and if so by how much?

And to follow up, if I go the route of road bike, are there any manufactuers who have a notable longer "cockpit"? Ya see, I'm 5'10" but only have a 30" inseam (actual stand-over height, not pants). When I sit at a table, I am always the tallest person. I think my torso came from a 6'3" guy as i can usually read (upside down) the name plate on the head tube when I ride most bikes.

So, what do you think? Do I make the plunge?

BTW: I have not ridden a road bike in 14 years, I was 23 years old at the time. Or is riding a road bike (and getting better with it) at 37 a pipedream?

Thanks,

ehenz