They aren't very good no matter how many you take, and not safe at high doses. Also if they contain APAP there is no simple way to remove it. 4 of them gave me a litte bit of a buzz. Not sure its safe to go much higher. Honestly, don't expect much.
Dextropropoxyphene is a remarkably crap drug. Although it is quite useless for pain, and recreation, it's lethal in overdose.
WHATEVER YOU DO, don't IV the stuff. It's a sodium channel blocker and will seriously fuck your heart rythm. Consider codeine instead, or if 2D6 deficient, dihydrocodeine.