So, thanks for the replies. I've been digesting them gradually ... and I finally got round to some measuring in the stable yesterday.
FOR ME, there are 2 reasons for asking this:
1 - Do higher BBs *generally* create problems? [for use in assessing future purchases]
I think the answer has to be "
Not necessarily!". I hadn't considered the extra wind-resistance, but I suppose it is a genuine-if-small drawback.
Mr interested made a good point, that CX bikes aren't generally the ideal purchase for general road use. But I think there are many different scenarios; for example, there are lots of old CX bikes on the 2nd-hand market to suit some folks' budgets, and there are some wierdos who don't want d**k brakes, and that rules out 95% of new so-called adventure/gravel bikes.
2 - Should I try using my Kinesis FiveT on the road (200km+ rides in particular)?
I almost certainly will after the main cross season, say Februrary-ish. The bike was probably designed as a compromise (e.g. has 2xbottle mounts!), so you'd expect it to work better as a road-bike than pure race-machines would. Now I don't fully understand frame geometry* but I have measured my Airborne Valkyrie against the Kinesis. [I've done many multi-300km-day rides on the Airborne.] The position of saddle, bars, head-tube etc is only a few mm different. in fact even the BB-height turns out to be closer than I thought [that's even on 33mm tyres vs 25!]
So I think as a negligible-cost experiment, it's a goer
*well I doooo ... but the combinations of factors are something I haven't totally grasped