Well my birding has just been curtailed somewhat. Yesterday the SDM on my DA*300 stopped - not a peep, no warning, just dead. Dropped it off today - it will take quite a while (5-6 weeks) to get it back they forecast and cost me ca. US$300 to have it repaired (it is 2 months out of warranty). So now I'm down to the Tokina 300/2.8 (doesn't seem to work well with TCs) or the SMC 300/4 (pretty old and pretty heavy) !
I'm now giving serious consideration to a D800E and a used Sigma 500/4.5 I spied in one of the shops in the camera mall today (with camo wrap it is US$1,500 cheaper than a new one for Pentax mount - giving me US$1,500 to go towards the D800E). Sell off the DA*300 and one of my K5s after the repair.