We have a glidecam 4000 for steadycam shots and we have ultra smooth manfrotto heads and tripods. No real need for IS unless we are going handheld, in which case we are mostly using the 24-105 F4 L IS lens. The 24-70 F2.8 I have right now needs to be sent in for a full rebuild and a lens cleaning (it is delaminating) so maybe that will help me a lot with IQ. IS isn't much of an issue for me
Then as I said, I'd just keep what you have.
It would have been interesting/helpful to know you had other lenses you were using besides what you put in your lens list - I assumed that was all you had to use. I thought of suggesting the 24-105L, but being an f/4 without additional accessory lighting I would think that it would often be too slow for weddings. I also (other than the 18-55) didn't know you had a FL lower than 28mm, or will when the 24-70 comes back.
So again I'd say work with what you have. Or (as I previously stated) add an f/1.4.
. He has the 24-105 F4 L, the sigma 30mm F1.4, Sigma 10-20mm F3.5-5.6 or w/e it is and then the 70-200mm F4
