Going FF - need to settle on a lens-logic!

[Daniel Browning]

Canon's 17-55mm IS f/2.8 and Tokina's 11-16mm lenses [...] I find myself using my zoom lenses in their fully extended or retracted positions the most (~90% of the time). I interpret this as a possible indicator that perhaps I should try my luck with primes instead on my next setup.

Well, your three focal lengths are approximately 11mm, 17mm, and 55mm. In full frame that's approximately 18mm, 28mm, and 90mm. Having one prime at each of those focal lengths seems like an excellent setup to me!

How about this?
Zeiss 18mm f/3.5 (manual focus, slow, 1 pound).
EF 28mm f/2.8 IS (not out yet, but only half a pound).
EF 100mm f/2.8 IS (1 and a half pounds).

Here's another possibility that's based on wider angles of view than what you had with the 50D:
Rokinon 14mm f/2.8 (manual focus, but cheap and 1 pound)
24mm f/1.4 II (1 and a half pounds)
85mm f/1.8 (1 pound)

The very lightest kit I can think of (2 pounds for all three):
EF 20mm f/2.8
EF 50mm f/1.8
Tamron 90mm f/2.8

[jrw]

One thought in favour of the zooms is less lens changing. If outside on a windy day will you really want to expose camera innards (sensor) to all of the dust and sticky pollen that is being carried on the breezes? You also mentioned starting with just 2 lenses, if that is the case will you have sufficient versatility for your shooting style with two primes?

Have 70-200 in f4 and 2.8 varieties. Like the f4 for landscapes, details not vistas, and critters in good light. Less weight is nice for longer hikes. Can not match f2.8 at dawn and dusk, for portraits, sports or anything else where shallow DOF or action stopping is desired. In terms of IQ, the f2.8 II is no slouch when compared to the primes in the same range. There is a reason why so many journalists and travel photographers use this lens. Do carry it on longer hikes when I think I'll want it with no problems.

Tele-extenders are a very convenient way to zoom in on a subject when you can't get closer. Don't make the mistake of thinking that they magically transform a lens into a longer focal length, as their use does come at a cost in terms of IQ. For closer subjects that fill most of the frame the difference will seem small, but if you try to use them with smaller subjects that are further away thinking you can crop down a lot you will find the loss of IQ to be more noticeable, especially with a 2x TE. Changing them in and out when on a hike can also present its own challenges, three objects to deal with and only two hands. We each find a way that works for us, but compared to a zoom lens it isn't as fast nor as convenient and exposes your sensor to dust more frequently.