i would skip the tamron, just because if you want that type of all-in-one solution, the S3IS will be there. as much as i would like to convince myself to buy that lens, i have a fuji s6000fd which fills that use perfectly (if only it had IS).
i have a very, very similar kit to your own. when i travel the kit i carry goes along in a crumpler sinking barge. it
always includes the 5D and 24-105. the 35L usually goes, and the 70-200 goes more often than the 17-40. the largest kit i like to walk around with for hours at a time is:
5D
16mm zenitar
24-105
35L
70-200
430EX if i see the need (rarely)
personally, instead of the tamron, what i would consider is either a 70-300 DO or non-DO. preferably the DO, since the build is much nicer and it is more compact. i actually had one, but it had issues so i got rid of it and haven't replaced it yet (of everything i've owned, this was the only 'bad copy' (i hate that term)). if you replace the tamron with the 24-105 and the 70-300DO, then you get better quality and 4 extra mm on the wide side... which IMO is a huge plus. the only downside is losing f/2.8, which would be unfortunate, but a travel kit is always subject to compromises.
so my suggestion is, assuming you are willing to by a 70-300:
5D
15mm fisheye
24-105
70-300DO
580EX
in addition, taking the 70-300DO in lieu of the 70-200IS and TCs will free up a bunch of room and weight, or allow you to carry the 17-40 or 35L (or both) if you wanted. for me, it'd be the 35L hands down.
of course, thats just my .02
--
ed murphy