The using the travel once per ride thing was kinda how we used to setup MX suspension, we were looking to bottom out on the biggest bump on the track, its a valid guidline, but better for something you do laps and laps of the same course.
On A MTB I think setting sag is the king, get that set right and you can ride around most other problems as long as your not miles off on rebound and compression (its only a pussh bike after all). Not sure about how much you need the rebound to be stopping your weight from bouncing about I thought it more for keeping the wheels from flailing about once its all unloaded, I stop myself from being bounced about by body english and being in the right position on the bike for any given obstacle.
As adeward says its about getting front and rear working together one end allwrong will mess the other up.
Dickbarton as you have changed bikes recently have you paid any attention to where your weight is relative to the cranks on the swap from your old bike to the new one? Could you be too far forward or backward on it upsetting the suspension?
Sadly the best setup bike in the world will only aid your riding, it isnt a cure, and more riding is the only way forward from there, and dont try to go too fast all in one go, up the ante gently at your own pace.