Is a A850/A900 still a good buy today?

First, I'm from one of the enemy camps (a Pentax user) but I'm not here in order to troll or fight.

I'm using older Pentax APS-C cameras - as opposed to having the new flagship K-5. For a long time I've lusted for a nice full frame camera from either Canon, Nikon or Sony. Now the Sony models are cheaper (especially the A850) and are better suited for using older M42 glass with an adapter. So I'm somewhat tempted. But considering for example the much talked about DxO Mark results, it seems that the newest APS-C cameras (with sensors from Sony!) have in many ways come close to or even exceeded these previous generation FF cameras. Judging by those results it seems that FF cameras are still way better regarding high ISO, but in for example dynamic range the new cameras beat them. Of course there is still the DOF control and in the case of Sony and Canon, also the greater resolution.

But as tempted as I am, I wonder if a FF Sony is still a good purchase today in your opinion if one hasn't yet bought into the alpha mount system? It seems very probable that Sony will eventually bring a FF of some sort (SLT, SLR, whatever) with a sensor of the new technology and that may well outshine any FF or APS-C camera today.

Thanks.