It's a pretty huge difference based on the ISO charts over on the-digital-picture. I'd go for a 35L over a 24L mk1--based on optical characteristics alone.
Ah, my bad, I forgot to mention TS 24. I know the MK II is sharper but is it sharp enough to really be worth it over the MK I? I found a pristine one for only $850 and the condition it's in is pretty good and I just sold my 5Dc, so I'm debating if I would want one.







