How do you feel shooting with plastic 60D?
Strangely, I feel more confident than when I bought it, because from experience I now know that if anything breaks it's the lens first, then the rear or top lcd. But more sturdy is certainly better, that's why I am quite critical towards my 100L "plastic" lens.
For my 2cents, I'd rather carry 100g more with the 24-70 and a sturdier body because 800g or 900g doesn't make that much of a difference, it's nowhere near my 70-300L or even the 70-200L
If you want heavier and slower, get the Tamron.
Excuse me, but that's bs - or are you implying that a lens can be either heavy/sturdy *or* have a fast af and good sharpness? No, it's quite alright for me to be critical towards the Canon trend to plastic quality (60d, 100L, 24-70ii) even if I own two of the said items.