24mm f/2.8 IS or 16-35 f/4 IS ??

I am considering the purchase of one of these lenses. I regularly shoot around f/4, 1/100 & ISO 3200 with my 6D/35 IS. The f/4 is to get sufficient DOF. Sometimes the 35 is not wide enough. I like IS on the 35 IS so much that I wouldn't consider the 16-35 II or 17-40. Not overly concerned with the price. I've tried shooting the same stuff with 60D/10-22 and don't care much for the noise at 3200 on crop, especially since I have a 6D in the closet.

EF 24mm f/2.8 IS:
useful FF & crop
$650 cheaper
smaller, lighter
f/2.8 available when I can use it
not much wider than my Tamron 28-75 2.8, but sharper & focuses faster

EF 16-35 f/4 IS USM:
pointless range on crop, already have 15-85 and 10-22
full UWA zoom range on FF
I can sell my 10-22 to offset the cost difference

I am stuck, although I am leaning toward the 24 2.8 IS. It is less intimidating in in-your-face, around-the-table type shooting. Is there anything I am missing that could sway me one way or the other?

OOPS! I forgot to add that if shooting wider I can open up and get the same DOF. DOF at 24mm - f/2.8 is about equal to 35mm - f/4 when shooting at 3 to 5 feet. That allows me to lower ISO to 1600 or raise shutter speed.

Ever since getting the 24 and 35 IS I haven't even mounted the 17-40 so I'm a big fan of both on FF. Paid $500 for the 35 and $400 for the 24, I won't sell the 17-40 because I do a lot of landscapes and need the extra FOV.

you'll never get 24mm to do 16mm. I shoot at 16mm a lot.