Hi Paul,
I ride in glasses, and only get problems when in flat-out chin-on-the-tank mode. Tend to get a problem with the top bar on the glasses cutting my vision. I don't find it a major trauma, and I don't get on with contacts so I haven't much choice.
If you choose glasses I should go with something quite large that looks crap but gives you a wide area of vision.
Cheers,
Ali