sorry, i thought you said your goal was 7.5 hours.
(I think that's a pretty good time myself)
The lessons from Raleighdon:
1. spend as little time as you can off the bike. Pre plan your stops, get your business done, get back on the bike. He's beaten many a faster rider simply by not wasting time at food and potty stops.
2. Do more hills. The more hills you do the stronger you will be on the flats.

Having said this, a road bike should speed you up a bit, but not a lot. The different angle you are sitting at alone will make you want to move faster.(happened to me, I can't explain it)
I was also told that the single upgrade to your bike that does the most per dollar is changing wheel sets.