I upgraded from the DS to a K-r + 18-55 kit. The five year gap in technology makes the difference really, really big.
I have considered the K-7 (wanting the build + controls), but due budget constraints, I had to get the K-r.
Having said that, if you 'got by' with the DS, the K-r is a dream to use. No more waiting 3 seconds to view your shots
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But I guess this depends on how flexible your budget is, and your kind of shooting. If you need a rugged body, the K-7 and K-5 are the options. Between the the two, if you need faster AF and high ISO, it's the K-5.
If you don't need a rugged body, then the K-r + better lens is the option.
I don't know if you've been following the threads, so a word of caution on the K-5. Better make sure you don't have the 'stained sensor' issue in case you decide on that. On a related note, K-r users are reporting FF in Tungsten light. My K-r exhibits that, you best read about it in the other threads.
HTH