azza, I have done nearly all my touring on 28 slicks, but also ride 37s regularly on another bike. My touring weight of me 140 tops, bike 30 and stuff around 40 comes to 210lbs. On good roads, 28s are fine, good roads meaning not bumpy, cracks and all that. With rougher roads, I would have liked 32s just as noglider says, you can run lower pressures and it makes a real difference in comfort from 110 to 100 or 90 or whatever.
I really do think that 32s are a good compromise, but it really comes down to how the "sealed roads" are, and you probably dont really know the condition of them unless you have ridden on them, so 32s seem to me to be a good starting point.
On the bike that I ride with 37s or 38s, I ride this bike more in the start and end of the season, ie much darker riding, more potholes (especially in the start of the season--this is a climate with -30c to +30c so road conditions are iffy due to freeze/thaw) so the 38s are nice not to have to be so concentrated on the road surface compared to the 28s, and are a fair amount more comfortable due to the lower pressures (again, nice when I start riding in the spring with my body not used to real bike riding).
If you think that the road conditions are good, I'd go with the 32s vs 37s, they may feel a bit faster or easier to pedal along with---caveat--depends very much on the specific tire you choose! Some tires are much lighter and more flexible than others, so have a very diff feel when riding compared to other tires of the same size.
If you think the pavement will be rough a lot, 37s will be nice for the comfort and not beating you up as much. I have tried 50s just to see how they are compared to smaller tires, and if I were to ride on really rough stuff, wider certainly is a bit cushier that could outweigh a slightly slower ride--Im talking 50s here vs 37/38s.
Given that you are a much chunkier guy than I am, I wouldnt go 28s just from the comfort aspect. In the end, its up to you to try diff width tires and see what you prefer, as you arent going for a while on this trip, perhaps trying out diff tires isnt a bad idea, and in any case, its always good to start a long trip like what you want to do, with new tires, so trying diff ones in the meantime isnt out of the question, and you can start the trip with new ones of the type/width you prefer.
Last edited by djb; 02-12-15 at 11:16 PM.