The pricing is right on this lens, easily worth spending the 275 over 17-40/4L.
16-35 II is a different ballgame though. If you are interested in doing indoor event work, IMO the 16-35 II f/2.8L is the better purchase; there simply isn't enough light at many indoor events to use an f/4 lens. In fact, often f/2.8 isn't even enough; f/2.8 is more useful in low light than f/4 IS at 35mm, and with shutter speed needing to be 1/100 minimum to freeze motion f/4 will hurt in the ISOs department. A noisy picture caused by five digit ISOs or motion blur will be much more noticeable in low light than less than perfect corner sharpness, and IS aside from not being as effective at wide focal lengths also will not freeze motion. I do have primes that are below f/2.8, but none of them at 16mm which can be useful in tight quarters like a dancefloor. The 16-35 II is one of the rare lenses that has a UWA-wide/normal zoom range, f/2.8, and accepts filters (I don't know how I'd feel with a bulbous element at a crowded event).
On the other hand, for landscape work this new 16-35 f/4L IS looks like an easy winner over the 16-35 II f/2.8.
So it depends what you are going to do with it, as is often the case IMO, 16-35 II f/2.8L remains king for now for event photography.
I'll definitely pick this one up, shortly after my daughter is born my bills are all in order... As far as the 2.8 vs 4 debate, i've been well vocal enough on this... and for giggles, as a weekend long event we were hired for to do photography coverage for, (all indoors) we played with different lenses and combinations... Needless to say, Regardless whether it was F4 or 2.8, we needed flash. And 2.8 made the DOF even more shallow and unforgiving than the F4 was to boot. In the end, i instructed my assistant photographer, and my wife and I to use our 24-105's. Had Flash, chewed through batteries but got a good thousand or so images after culling that were sharp, ISO was ok (manually set at around 4000 which on our 5d3 and 6D came out gorgeous), and flash... I personally feel the argument that you NEED 2.8 for indoors is just wrong. If F4 cant pull it off, 2.8 really isn't going to buy you much latitude, and you have a narrower DOF. 1.4 and such is even tougher with DOF, especially for event coverage. It's good for artistic expression and isolating subjects, but shooting groups of people, shooting moving subjects, shooting events, you will likely still need flash or ISO to get good shots, and with modern cameras, ISO is becoming even better. I've had indoor wedding shots around 20,000 ISO that came out gorgeous with minimal noise... It is what it is.