Trade TS-E 24 mk1 for UWA zoom

Hi all - I've enjoyed using the original TS-E 24mm for a year or two now, but am feeling a little restricted by it, and only very infrequently using it to correct for converging verticals, not tilting at all. Landscapes and seascapes very rarely seem to be affected by the UWA perspective change, so I'm making a conscious decision to move back to an UWA zoom lens, but would really prefer to stay away from the F/4 items.

I haven't looked at the options for a while - I used to have the 17-40 which was great if not quite as sharp as I'd like. I'd be selling the TS-E and looking for a direct trade to something - I should think I can pull in around £750 ($1200) so what would you opt for given my circumstances?

Thanks

There is the 16-28mm f/2.8 Tokina, but it doesn't do filters without expensive adapter. It is about the same as in price as the 17-40L.

Or there obviously is the more expensive Canon 16-35L II.

For scapes though, I don't see the f/4 being much of a detriment. The new Canon 16-35 f/4 looks awesome, and IS is a nice touch. I will most likely go for it, if I can get somebody to bite on my 17-40L. I will not take a big hit in price though, and now that is what everybody seems to want. I will keep it for that. It is still pretty darn good wide open and even better stopped down.