Change Canon 18-135 for Tamron 18-270 PZD

Note - I hae also posted this on the lens forum. Has anyone any real life experience of both these lenses? I am downsizing (making lighter and smaller for travel, hiking etc) my 60D and 18-135 Canon to a 550D and Tamron 18-270 (new type PZD).

I have the 550D and am happy with it - the Tamron appeals because of the smaller size and longer zoom. I have always been very happy with the optical performance of the Canon 18-135 and am concerned that I may be degrading this by moving to the Tamron. I wil print to A3 (about 16" by 11") and shoot everything in RAW, processing in ACR and using the lens correction function (I occasionally use DPP and expect that it will not offer lens correction for the Tamron).

As background I also have a 5D Mk2 and 24-105 - the 550D and one solution lens is intended as a more portable / travel set-up.

I have looked at the various test reports of the two lenses, but would appreciate input from anyone who has used both lenses.

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Best regards
Vince C