[clickclick]

The 24-70 is a nice lens and handles well on the K-1. I find it a really good feeling combination in the hand, and not too heavy to throw over the shoulder and go off with. You also have WR. I'd be tempted to say go with that but hold on to your other lenses. If you have to wait longer to save up more to make that happen, then do so. You might find in certain situations you want some other combination. It's nice to have options. It will also help with LBA.

[mikesbike]

In your own shooting experience, how often do you need to switch to your 19-35mm Lens because your Tokina 28-70mm is not giving you enough width and you'd benefit from its having a 24mm FL? Also, how often do you need that f/2.8?

I have a similarly fast f/2.8 zoom lens on my APS-C outfit with a similar FOV as your Tokina lens on your FF body, but I don't always use it. I often carry a smaller zoom lens instead because I'll be working in good lighting, and not dealing with fast-moving subjects. If your situation is similar, you might consider the very fine-performing DFA 28-105mm lens for most of your needs, its being lighter, having a fast, quiet AF, as well as WR, and then take out your f/2.8 lens instead mainly when you need that speed.

The DFA 24-70mm f/2.8 is indeed a fine lens, and the fine differences are there, but often times when an actual image from both lenses are put side-by-side it is difficult to actually see a difference. This might very well be true if comparing images from your Tokina lens and the DFA 24-70mm lens. The practical value would be in having that 24mm capability along with WR. But with the DFA 28-105mm you'd be gaining considerably more reach and carrying less weight.

[niblue]

My most used lens is a 24-70mm F2.8 zoom. I personally find that 24mm instead of 28mm at the wide end makes in a huge difference in usefulness - so I'd much rather have a 24-70 instead of a 28-105, although that of course relates to my own personal preferences. I also don't put a lot of weight on WR for lenses either (I've shot a lot in the rain with no WR lenses and never had an issue).

In my case it's not the Pentax lens, instead I'm using the Sigma 24-70mm F2.8 which is a very decent lens and can be had very cheap in comparison to the Pentax lens. I'm sure the Pentax will be a better performer (and I might indeed get one at some point) but in the meantime I've been very happy with the Sigma.

[clickclick]

24mm instead of 28mm at the wide end makes in a huge difference in usefulness

I think I have to agree, when backed into a corner, literally. Just having taken some family table shots at Thanksgiving is a reminder I can't back up, but I can zoom out.