6D vs 5D2 vs 5D1 for TS/Landscape ONLY

Hi all,

Since there are no viable tilt-shift options for Pentax, I am looking to move to a different system (ONLY) for my Tilt-shift and landscape photography. The Mk1 24mm TS goes for less than £600 and a 5D mark1 goes for £500. For use with the 24mm TS and maybe a 17-40, would the 5D2 or 6D offer major benefits when shooting at ISO 50-200, and MF? Does the 5D give acceptable IQ, and how does it compare with an APS-C like the 7D, and is the 5D to 5Dii jump worth it?

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Angad S. aka gooseta
LBA and CBA haunt me.
angadsrin.zenfolio.com
X100 black
K5iis, K-01 with Sigma 8-16/4.5-5.6, M 50/1.7, Sigma 70/2.8 macro, DA* 300mm/4
Leica M9 Grey, 50 Summicron 1988, 21mm Elmarit preASPH, Voigtlander 35mm f1.4 Nokton
Pondering a 21, 31, 43 system or a 21, 35 macro, 43 system