How fast?

[alpinerabbit]

I think you should shoot for 20-22 mph.

just kidding...


.....
Not knowing the terrain, the bike or your fitness level, I don't think anyone can tell you "this is how fast you should be going".

So don't go by speed, but by heart rate or exertion level, and compete against yourself, or others. Looks like you are doing that by shaving off time.
Go at a good clip, attack the hills, come back refreshed one day or knackered another. You'll get better. Try riding with others to figure out how strong you are.

Re: training plan, ride differently: easy a couple times a week, hard (think intervals) another couple times. Vary the routes. Don't do the same thing all the time, that will just make you fit to do the same thing all the time.