Originally posted by Hmm So Tamron lens' isn't very good these days?
Tamron makes some excellent lenses. So does Sigma. Here is a link to the
Tamron lens database with user reviews. Your 100-300mm is not rated very highly, nor does it have great specs, it is an economy level long zoom. And remember each manufacturer has lenses aimed at different markets and price points, some are really good and expensive, some not so good but cheaper. But my point really was that if you only have that single Tamron in Pentax mount you really are not heavily invested in Pentax gear and can choose which ever DSLR fits what you want.
On the one hand you state you are looking for a good deal and are a bit of a cheapo and then on the other you ask if you should wait for full frame. Sorry, but that seems a contradiction to me. Full frame in DSLR is very expensive, used mostly by professionals who make a living at this, usually accompanied by glass that costs more than the camera, and unfortunately non-existent in Pentax mount despite all of the wishful thinking that goes on.
If you are looking for a good DSLR that can produce good images without a lot of input from you then look at the Pentax entry level camera, the k-r or its probable replacement. If you want a solid semi-pro or enthusiast level camera with complete manual controls then the K-5 is where you want to be. But it is an APS-C camera not full frame and the smaller sensor does affect your lenses if you are used to the field of view shown in a full frame camera. And if you really want full frame, either look to Nikon or Canon or be prepared to wait to see if Pentax ever releases such a thing. And be prepared to invest multi-thousands in good glass or you would have been just as well off with a much cheaper camera.