Thank you all for the input - I hadn't even thought about the possible weather delays....I did have an express to catch at Ostbahnhof - the next one is an hour and a bit later - I'll go for that one - I didn't want problems with specific trains on tickets and trying to explain to a Db ticket inspector. Too much stuff just for cabin baggage.
Just for info - anyone traveling to Frankfurt - it'll be a long wait just to get your passport stamped...not to mention walking about half a mile - I am exaggerating a little!