In reply to lizard-16-07:
I'm also 5'1" and have similar size proportions to you...I got my road bike from Evans where they took my measurements and cycling position and let me know which bike would be suitable for my size and reach, so I'd recommend going in there and getting some advice.
I ended up buying a Jamis Ventura Comp (Womens) in 2012 and have a lot of praise for it. Good spec at a reasonable price; I paid around £650 after adding SPD pedals onto the bike. I find the bike is nice and light and you can get good speeds from a static position, but is steady on the longer rides too. The dropped handle bars seem to have an extra 'curved' structure and allow for different positions when riding which is good. Also, as you want to do longer distances, the saddle is surprisingly comfortable, and I don't tend to wear any padded shorts as a result!
Good luck!