I don't believe the dv affects compression unless it is worn or basically stuffed. They do seal up pretty good, like any valve should. When the motor is running the valve does not pulse but rather stays closed all the time. The High comp head will deliver more torque. If you want maximum grunt with no possibility of compression being affected in any way use a high comp head with an old spark plug blocking the hole but be prepared to dislocate your shoulder once in a while and replace the starter rope a lot more frequently.
