Depending on what the RRP is of the non IS f4 lens as a bench mark I would say that this isnt worth it, prices should fall pretty quick once its released, but as it is at the moment I dont think paying twice of the 70-200 f4 "non" IS is worth it, most people would prefer to hunt for the 2.8 non IS or perhaps even pay another £100 to £300 for the 2.8 IS (where funds allow).
All IMHO but I think Canon are screwing with a lense in which the clincher is the fact its high quality at low price, IS is worth alot, but I doubt its worth £500 more.
However I suspect the first price (£689.99) will be more in line with what this lens will settle at, alot like the newly released 17-55 f2 IS which was quoted at a grand+ I beleive when first available, and is now going for less than £700.
Excuse the rambling
