touring tyre advice

The only real difference will be comfort - the narrower tyres will feel quite a bit rougher on the roads.

The Marathon Extreme is supposed to be the replacement tyre for the XR - its a lot lighter, but it seems Schwalbe are confident it can match it for toughness. I just got one, but haven't fitted or tried it out yet, it does feel a lot lighter than an XR.

I wouldn't recommend 1.6" tyres for the Himalayas if you can get decent wider tyres. The difference is not just comfort - many Himalayan roads are extremely rough and it's nice to have grip when one is close to a >1000m cliff on a rough, loose surface.

FWIW, I used 1.4" Crossbites for the KKH in 2000, and had to inflate them pretty hard to prevent pinch flats; they did grip well though. In 2006 I took the 1.9" version to Himachal Pradesh, and had many, many punctures. I found that Maxxis Larsen TT 2.0" MTB tyres rolled well on road and off, and gripped and cornered well everywhere. They are not, however, extremely puncture resistant, and for Himalayan back roads I'd be inclined to take the 2.35 versions to ward off pinch flats. (I was stupid enough to participate in MTB Himachal and the number of pinch flats suffered by just about everyone on the very rocky roads chosen by the organisers was unbelievable.)

Last year I rode from Manali-Leh, then around the Nubra Valley, west from Leh, etc. I used a lightweight front tyre and a 2.0" Marathon XR on the back. (I had ski touring and winter camping gear and could not take a bike to India as well, so just took a few parts, foolishly expecting things would have improved since my last visit.) Had no problems until after the Taglang La, but then things got worse rapidly. Be aware that after the first village past the pass onwards there are bad thorn problems, also in the Nubra Valley. I got my only punctures in the XR here. (Really only one, but then problems with repairs and spare tubes.) I had at least 7 holes in the front tyre from the first incident(!).

Moral: take very puncture resistant tyres. The XR was good, and the other guy I rode with in Nubra used them and had zero issues. I think the Extremes would be much better for Ladakh than XRs as road surfaces there are often/usually loose and/or wet, so more grip wouldn't hurt; if they're a bit more supple and roll better too, that would be an excellent thing!

Be aware that it is almost impossible to get anything but Dunlop valve tubes in India, and take an adapter to pump these up, plus some easy-pump valves; the latter do not exist in India. Decent parts are still *very* hard to find in India, though much more possible in Kathmandu. However, touring tyres, tools, racks and panniers are almost unobtainable. In fact, decent tools of any sort are almost non-existent in India IME. Get everything you need beforehand!!!

Lastly, I would try to catch the bus to the top of the Rohtang La from Manali if going that way. The traffic there is unbelievable, both in quantity and in (lack of) skills and consideration. And it started from Manali last year from ~4.30am and continued until after 8pm some nights in the other direction.