+1.
Ribble have their own sizing system. They ask you if its Horiz' or sloping and measure C/top.
Read their sizing instructions very carefully.
I opted against Ribble. I wouldn't buy a bike which I couldn't stand over before I handed over the cash.
I got a Dawes Giro 500 mail order, but I went to a shop in Coventry first to see one in the flesh.
Ribble do some good deals, and IF I did buy one, I'd take the trip to see them first.