That is exactly the lens in question. I have used it on the 35mm and I do notice a lot of hunting and slow AF. I have certainly missed some shots that way. When it does work the picture quality is fine for what I am doing. I have always believed it is all about the glass and I am sure I will want to move on from that lens. The financial issue is if I go with the Nikon I have to do it right away, with the Pentax I could start with that lens and then wait.
There are pros and cons to either approach. I've noticed that lenses are in shorter supply in Pentax mount looking through used listings. They tend to be a bit higher priced in Pentax mount, too (especially brighter primes).
However, it sounds like you really only want one lens right now (somthing to handle your soccer games). Since you already have some Pentax lenses, that may be a way to approach it (buy a better lens later when budget permits), provided you are happy with the model otherwise.
On the other hand, you could always buy an inexpensive used lens for another mount, then replace it later when budget permits, too. I'd also check out the lenses graded as "Budget" at KEH.com if you go that route. They tend to be very conservative with their lens ratings (and they are guaranteed to work with a 60 day warranty). So, you may be able to get a cheap "temporary" lens to tide you over.
So to my eye those numbers look awfully close, the biggest difference is the time to flush the buffer
Autofocus times will vary a lot, depending on the conditions, lens, and subject. So, don't assume that the times you see will be the ones you get. AF can be slower. Of course, there is always Manual Focus if conditions are such that AF is not reliable enough. ;-)
Also, since you mentioned shooting raw, buffer flush times will be much longer. Even with a Sandisk Extreme III SD card, after a burst of 5 raw images, you'll need to wait about 15 seconds before you can take another 5 shot burst with the Pentax.
For most users, JPEG would probably be a better way to go for sports (more images in a burst, faster flush times).
In the end I suppose it will come down to budget. I could buy the Pentax and save for a really good lens or go with the Nikon and have to spring for lens's immediately.
Try them out in a store. Also, look at the used lens market and see what lenses are selling for to help make a better long term decision in a system.
Good sources for used lenses are http://www.keh.com
and of course, http://www.ebay.com
A good source of lens performance is http://www.photodo.com
(make sure to see 3rd party lenses from Sigma, Tamron and Tokina, too). The ratings there are based on MTF tests (which are not subjective) versus user opinions.
However, you want to take user opinions into consideration, too. MTF tests never tell the whole story. You'll want user opinions on things like color, contrast, af speed, ergonomics, build quality, and resistance to flare. Make sure to test drive lenses you consider in a store, too (there can be a big difference between how they work -- zoom mechanism, focus ring/design, etc.).
A good source for user opinions is the Lens Performance Survey database you'll find at http://www.photozone.de
(and the Lenses forums here, too). You'll see dedicatedforums for Nikon and Canon lenses here (but many third party lenses are discussed, too).