Decision Time - 24-105 or 24-70 f4 for 6D - INPUT PLEASE !!

Hello,

I have decided to upgrade to the 6D from my lowly XTi.  I currently use a 17-55 for travel / landscape / a few portraits and love it. IQ, contrast and color are great - as we all know.

The 6D kit w/ 24-105 is $2699 from B&H (a good deal).  I've read good things and not so good things about the 24-105. I know this lens has been out quite a while (as has the 17-55) and I don't want to compromise on image quality noticeably.  I'm not concerned about distortion ( I shoot RAW and process in LR4).  The f4 max aperture is not a concern really with the ISO performance of the 6D (especially coming from XTi!)   What does concern me is sharpness and local contrast - will I be disappointed with 24-105 coming from 17-55?

I've considered the 24-70 f4 and could swing it but from the few reviews I've read thus far it sounds like a modest improvement on the 24-105 and not worth double the price of the 24-105 (in 6D kit).  But I do not purchase new gear often and would rather get it right even if that means paying more.  But since the 24-70 is a shorter lens on FF than 17-55 on crop (70mm vs 88mm) I think this focal range might seem limited for a general purpose walk-around lens.

I would appreciate if any of you who have used 17-55 and 24-105 (on FF - as I understand there is an IQ / sharpness difference using 24-105 on crop vs FF) could give me your impressions or advice.

CZAHAROP

PS - My other lenses are 70-300L and 10-22. I am thinking to add 16-35 II as a UWA if I upgrade to 6D.