Here's what you might regard as the "nutters perspective" But here goes.
I have done a bit of touring - mostly on roads, but did the Tasmanina Trail on an early model Repco Tracer - no suspension. Budget bike. Basic everything. No mods at all apart from 190 slicks. These gave me enough contact area and squish to accommodate bumps and little nasties and were smooth enough to crank it up on the tar, when out on the bitumen. Big tyres are really helpful. Only downside is on greasy wet clay surfaces and small well worn gravel (ball bearing like). They are, however, generally available.
Recently, I've even gone bigger. Surley Pugsley. (370x26) With this, my regular tyre pressure is around 25 psi, 30 max. The ginormous tyres don't give a lot away. Consider they are mostly air, much better off the road. People say they run them down to around 12-15 psi, but I'm not a fan. Really low pressures flex the sidewalls a lot and it's a little more work to ride - starts to compare with tyres with big lugs. At 30 psi, you can still ride across a beach, and not a lot is gained by dropping to 15, though at that pressure they are really compliant and soft to feel. The big Endomorphs are not heavily lugged, rather have a chevron barred pattern with lugs on the edges only, so on a hard surfaced road, you are not wasting energy deforming lugs, and the lugs give good lateral grip when the camber is against you or you are climbing out of a groove. I have yet to get caught out by either of these on these tyres, though I'm not saying it can't happen. I haven't used them when it's wet and slippery yet. I am anticipating a degree of "float" over mud, rather than the sink 20-25 cm and bog I am accustomed to on 175x26 tyres.
It's early days, though, and I'm thinking probably I'll settle on 20-25 (probably more like 25) for regular use. This seems the best compromise for the kind of riding I do. What's that? Level (ish) bush tracks and single track trails, in and out of creek beds with 3 and 4 metre rises and drops. a significant advantage of the big tyres is the way they just hang on when going down a steep drop with a turn at the bottom. Comes down to nerve, really. So far as I can tell, there's no significant penalty coming out. They are not so big you can't crank them up to make the rise back out, and have the advantage of being less affected by the condition of the track, sticks, rocks etc.
I'm a fan of big tyres. I think I'm realising advantages that a suspension just cannot provide. The downside is that they are not generally available, and are expensive..
I'm convinced, big tyres are of more benefit than suspension, if you are not going to be going hard downhill trailriding at least. There is also no extra mechanical complexity and wear issues which will eventually affect suspended bikes.
My opinion only.
ime confused about this i will be going to cannock chase if this helps please help ime reli confused 
