If you are going to project, I would use Kodak E100G or E100VS, also Fuji Velvia. All these films will project well, but do not expect the exact same results when scanned.
I assume that you will be bringing these films back home to process as this a long trip, people have mentioned X-ray scanners, I wouldn't worry about them unless you plan to bring films that are 800 speed or faster.
I will recommend that you use a processing house that will process, scan, and mount all at the same time, you will get far better results than if you try to scan later, or yourself. Unless you are lucky enough to live close to a place that does E-6 in house plan on about a two week wait for the photos to come back, and with the films I have mentioned above it will almost be like you are there again.
If you insist on using Kodak Elitechrome or Fuji Sensia, because of availability or cost, I would go with the Sensia. I want you to know that I will almost always pick a Kodak film over a Fuji film, but in the case of these two films Sensia would be the way to go.
Enjoy your trip.
If you want the Velvia for the saturation, shoot it at 40 instead of 50 - it takes it from ridiculously over-saturated down to just punchy as all get-out. With light being as intense as it is in that part of the world, I'd frankly opt for nothing faster than 100 speed unless you know you're going to be shooting a bunch of night shots hand-held. This is in part a personal preference, as I like to be able to shoot in full daylight without being stopped down to f22 all the time. Especially for people shots, it is nice to be able to throw backgrounds out of focus to at least some degree.
No sorry Scott, Fuji Velvia like all colour reversal films because they are posatives and aren't subject to the negative /positive process, and if you down rate the ISO film speed the resultant transparency will be less saturated not more as in negative films, i.e. if you wanted more saturation with Kodachrome 64 you shot it at ISO 80 for more saturation not ISO 50.
I shoot a lot of Velvia and I find it plenty saturated at the boxed speed, and should think that in the lighting in Southern India Velvia should knock the viewers eyes out.
The more exposure you give to slide films the lighter the resultant transparency is., that's why they are called " reversal films"
Benji- that's what I said- down-rating it will take the saturation from eye-bleedingly over-saturated to merely intense. Either way, the colors will still border on the un-natural, especially the greens, but will be less unnatural at 40. I would personally prefer something with the color saturation and palette of Ektar 100 but they don't make that emulsion in a sllide film.
Sorry Scott I misread your post, actually Fuji Astia is the least saturated slide film that they make, then Provia, and the most saturated is Velvia.