Spotted...

Slight derail, but a question: what ratio do you run? I really have to up the 48/18 gear on the Bob because I've been riding the Feather this week at 47/17 and it feels quite a lot quicker, and no more bother on the hills mild inclines like Pentonville Road.

What I run isn't really important (I'm on 48/19) but it sounds to me like you just need to spin more, not gear up. I don't know what 'bother' you are having on the Col du Pentonville, but I can hit 34/35mph on 48/19 so you should be able to go north of that. It's a 30mph zone anyway ;)

And yes it has been said a million times but not without good reason: pushing around a silly high gear does involve a high probability of breaking your knees. You may be ok, you may not. It's risky.