Is a 51cm frame road bike the correct size for someone almost 6ft?
From the website:


  Large bottom bracket to top tube = 51cm which is equivalent to our standard 58cm frame


51cm sounds too small for you; 58cm might be ok or it could be too big.  But there is no substitute for actually trying out the bike, or at least something similar to it.  Your leg, arm and torso lengths all have an effect on how well any bike will fit you and it's based on more than just the seat tube length.

Remember that a bike that's comfortable and fits you well will be more fun to ride.  Good fit is more important than weight or colour -- or even price -- so choose wisely.