Most of my close friends - Straight (late 20's) have done the SR->PP->Sr (or vice versa) overland route
I have also done the Arranyarathet/Poi pet->SR overland route myself twice
All of us heartily recommend against going overland to anywhere to Cambodia
Just fly!
And if you can't afford to fly - you shoukld just stay at home... and save till you can afford to travel in relative comfort
(or at least until they put tarmacadam on the roads!)