I can only tell you about the 17-70.
I bought this lens recently together with the K-5 kit. It's better than the kit lens, which according to photozone is roughly equivalent to your 18-135. How much better than the kit? Not much, to be honest, unless you're pixel peeping. It's a bit better wide open, has sharper corners, and doesn't lose as much at the long end. I prefer it because I like fixed aperture lenses, but center resolution at optimum apertures is about the same, which is true for many lenses.
I was debating between this and the Tamron 17-50, which may be a marginally better lens and adds a stop of light, but the K-5 high ISO performance is so good I opted to go for the 17-70 because I wanted the SDM and the slightly longer focal length. Since you have the 18-135, the difference in aperture to the 17-70 isn't much, so I'd skip it and explore the f/2.8 options.
|Dirt Hose by poppyjk|
|European bee-eaters by drvanger|
from A Big Year - birds
|Fat Is Beautiful Guinea 2008 DP by MarioSS|
from - Fat is Beautiful - (Woman's Portrait n Black and White+ A Border)