Thanks for the replies so far.
The OR Ferrosi has certainly piqued my interest; two recommendations here and a pretty glowing review from outdoorgearlab, which actually mentions the hem length:
http://www.outdoorgearlab.com/Softshell-Jacket-Reviews/Outdoor-Research-Fer...
The wind resistant vs windproof is not a huge concern as I believe the Pertex Equilibrium is the former too. I don't find that hugely wind permeable, so if the Ferrosi was comparable I think that would work well.
Nathan79, I find the problem with cycling tops is that they have decent length to cover the arse, but are cut short at the front to account for the crouched riding position. That, and the fact they tend not to have hoods. Appreciate the suggestion, however.