Best thing is have a play. Take some shots at say F5.6, F8, F11 etc and you will find what you are looking for. If the background of the subject is close, then you will have less blur, but if it is further away (and it can be a metre or so), then the blurred effect will come into play.

Colin, you say that you shoot mainly at F5.6, would this mean 300mm at F5.6 too?
Longer focal lengths will provide a shallower depth of field than shorter lengths in relation to its field of view, but it is too complicated to state here (hyperfocal distance, Distance or closeness of subject etc etc). So 300mm will have a very shallow relative DOF at F5.6. However by stopping the aperture down to around F8-F11, not only will you find the lens sweet spot, but will also still have the blurred background that you desire and have more of the subject in focus.

Hope this helps.

Colin I have the non-apo version and a 170-500. I had the same problem where images are either soft or spot on.
The other week I went to a nature reserve and took some shots of the squirrels. Rather than fixing the ISO, I let my K20D choose the ISO, after I had set the speed (1/100 sec) and aperture (F10), the camera was also on a tripod. Each shot was nailed.
However I have noticed that the K-m does not have TAV mode, only Sv. But maybe manually fixing the lens to F10 on the ring, selecting a high ISO (800-1250) and letting the camera do the rest. It might help.
link

I did look at this when it came out last year and it was intriguing.

However there are three things wrong with it.

1. No RAW
2. The aperture is either wide open or closed down. No steps.
3. Widest aperture is only F3.3, whereas the "pro" compacts are faster (Panasonic is F2)

What is more impressive is the F300EXR, which is the F200 replacement. Smaller sensor (shame) but they have put a clever phase detection AF (a first for a mirrorless camera) rather than contrast AF. Now if it works, I can forgive its lack of RAW, slow lens, and silly stepped aperture.

Still, I would rather Pentax came out with a decent spec compact.

I have just done some investigation for some friends, and the reality is that this market is far from being swamped with cameras.
At the moment, the only cameras which meet the spec are the following:-

Canon G11 and S90
Samsung EX1
Panasonic LX-3 and LX-5.

Nikon did have the P6000 but that is discontinued.

So, I would say there is a market for a Pentax model, as I am sure that they would sell pretty well.

The interesting thing though, that far from being a compromise, certain pros have this type of camera with them too. For instance, the celebrated landscape photographer, Joe Cornish, not only has his Large format and DSLR, but also a Panasonic LX-3 which he rates highly.

I have noticed that too on my DS. Not that I mind though, and it is pretty accurate metering in Av mode.

Funny, but Dimitrov's web site says that the MZ50 wont take none A lenses as the mount is crippled.
However I have an MZ50 so will put some batteries in it and see if it will will meter with my manual lenses.

I have very occasional (and I mean very occasional) AF issues with the 50-135mm, where is will not focus in either AF or MF. However by switching the lens with another and switching back, it works. It is a fault, but not to a point to affect me at the moment.

If Raleigh did lenses..........

Its in sensor speak rather than precise measurement. It stems back to vacuum tubes.

What I did miss was the 1. bit, so should have read - 1/1.7" and 1/1.63" Sorry for the confusion.