I’ve done Manchester – Liverpool – Manchester on the trans-pennine trail a few times, on a road bike with 23″ tyres. Very variable surface, lots of stones, gravel, small rocks, glass etc. No problems other than one puncture. Good tyres are as important as the bike though. Cross tyres tend to have very little puncture protection for things like glass etc and have a lot of drag on tarmac, best avoided. I’d go for the Continental Gatorskins which are virtually bullet-proof, but still ride very well. That said I would +1 the guy who said the Surly Cross Check. Had one of these until it got nicked and whilst it is a tad heavy it’s lovely to ride (Surly are the same company as Salsa) and just steamrollers through everything. It’s got clearance for big tyres and you can run a rack on it and mudguards no probs. If I had to have one bike for everything it would probably be that, as with fat fat tyres on it, it would be into 29er territory (sort of). If you want a great alu cross frame, look at the Kinesis range, they consistently get good reviews, but if I was you I’d check for rack and mudguard mounts.