That one is really hard to answer without knowing what you already have.
You seem to be a well known guy here with 3.300 Messages, but may I humbly ask for a link to your work? Maybe that helps giving a suggestion about what lens might improve what you usually do, or give you new possibilities.
That said T&S has been on my list for ages. I too love the possibilities (during my education I worked with large format with bellows and loved it. I still own a sinar p that I bought used for practising back then, but it collects dust). I particully like the macro effect, that you can achieve with wideangle T&S on 35mm.
On the other hand I absolutely love the 70-200 f4. It is reasonably light, and sice I'm travelling a lot that is way more important for me, than the 2.8 aperture, that would not only come with a much bigger price tag, but also muuuuuuch more weight. I am totally happy with it wide open.
BUT: I own a 7D, 5DII and 5DIII. I NEVER use the 7D. So I'd vote for full frame, but perhaps not the 5DSR that never challenged me to upgrade.
Well my current lens lineup is:
Canon 10-22mm f3.5-4.5
Sigma 17-70mm f2.8-4
Canon 50mm f1.8
Canon 135mm f2.5 (with a hard conversion from an FD to an EOS mount)
Tamron 150-600mm f5-6.3.
Normally when I go out I just take my 10-22mm and my 150-600mm.
You can see my shots on flickr at
wee_pete’s albums | Flickr
Thanks for the insight

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I particularely like your scottland shots - really makes me want to go there one day!
Hmmm - having looked at your portfolio, I don´t see too much use for a T&S Lens unless you want to change your main subject. If you want one, you might rather think about a cheaper third party, like the Walimex 24mm f3.5. That one is much cheaper and for the few occasions you´d like to use it, I think you don´t need the utmost quality.
I think the 70-200mm would fill a gap somehow, especially since you say you only take two of your lenses with you. But may I suggest another lens? 24mm f1.4. The shallow depth gives some really nice options when getting rather close. I think that would fit your shooting subject and easily give you a new look. I don´t know if it is wide enough for your landscape use on a crop sensor.
Upgrading to fullframe doesn´t really make sense because you would have to get a wideangle and a standard zoom to replace the two lenses you have.