The K-x or K-r would be an upgrade if you require iso 1600 + 3200.
Don't pay attention to DXOmark... their tests are more or less misleading for the average photographer. Statistically significant does not equal artistically significant

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You will likely notice it to be a "downgrade" in build quality and external features.
Between the KX and KR, I would select the K-X because they can be had for so little. I tend to buy the previous generation, though, because I believe that is where you find true value.
In fact, the K-X and K10d would make good companions. I believe the K10d would be better for iso 100-400, and the k-x would be better for ISO 800-3200.