I'd say it sounds like a K-7's the ticket, barring a K-5 purchase (I wouldn't buy some claims that's a generation behind the Nikon competition: they're about the same, and Nikon's had to undercut on price to compete that way: anyway, no fuss there. You'd have to evaluate each on strengths and weaknesses and preferences and purposes. I wouldn't buy into the grousing and brand wars on this: a lot of the gaps are just closing, anyway. )
Depends what glass you have there, choosing between brands, though: it seems you're sitting on a perfectly-good stable of both. Nikon's lack of compatibility with older glass unless one bought a sixteen-hundred dollar body is probably a big reason I'm here: a K20d came along for a grand less than a D300: by the time the K-5's price comes down within reach,, that'll probably be all the performance I personally need. (And then cause I mostly prefer low-light, anyway.
)
The K-7 shutter is quieter, by all accounts, (To me, 'Quieter than a Canon FTb' is quiet, so what do I know.
) and there's a slight edge in AF and high-ISO there over the K20d, so it may be an option, Not being a bird shooter, (unless you count occasionally stalking around my backyard with a cheap old manual zoom or a 135
) it mightn't be enough difference to trouble with for me, compared to a K20d, but it does sound like a K-7 might be a decent choice for you. They've already done the lion's share of their depreciating, so you could upgrade later without taking too much of a hit.
If I had a pile of old Nikkors and a trusty F3HP and FE, I might bide my time with Pentax a while and see what a D700 costs in four years. (Or I'd just be starting to look at used D300's about now instead of having a few years of K20d. Me, I was a Canon FD holdout with a Lumix FZ-7 having mad fantasies about them throwing us a 'Digital Back FN' or a 5d with FD mount. Nikon got a fair shake, especially considering I had a line on some old Nikkors: I just couldn't make the numbers work out, and ....Pentax glass.
)
As of now, it seems a lot of the tech gap is just closing, for anyone used to film's purposes, anyway. Pentax glass is somewhat pricier than it was a few years ago,, and some of Nikon's useful bodies are starting to trickle down within reach of the plebians: it's down to what you need and like. Nikon would have a hard time dislodging me from here, now, (Especially cause FA Limiteds, something to put behind them, and a truly stellar/precise focusing screen are about all I'd really ask.
)
Anyway, I ramble, but you could just get a bit more current and be on your way for the time being. If you're still shooting a K100d, you're *probably* not impressed by 'who's winning' various marketing races.