Well I think the 50mms focal requires you to be quite a bit further from your subject to shoot.
THe 17-55mm is not macro capable so you cannot do close up shots if thats what youre thinking. Its min focal distance is 0.43m so thats how far you must be away for your subject. In this regard the kit lens 18-55 IS is better because it focuses at 0.23m away from the subject.
Other than that the 17-55 is alot more versatile in a restaurant than a 50mm for food and guest shots.
You have to try and see for yourself, but from what ive seen. the 17-50 VC is a drop from the non VC, which is very sad, because the non VC was soo darn good.
You pay $600+ for the non VC and 300 more for VC but with a drop in IQ.
If you dont need Image Stabilisation, get the 17-50 Non VC. If you do
. well what i did was get the 17-55 but its quite quite hefty in price indeed.
Well if you got a 70-200 f4L
IS youre prob well off enough to shoot for the 17-55 no?