SD pen usually expressed in "Rule of --"
Rather than trying to estimate single deck pen in percentage, use the standard single deck "Rule of --" that the casinos use.
"Rule of 7" means 7, minus the number of hands being played = number of rounds to be dealt.
"Rule of 6" means 6, minus the number of hands being played = number of rounds to be dealt.
From the BJ21.com BJ Glossary:
Rule of six. A policy followed by many casinos at single deck. They require a dealer to deal five rounds to one player, four rounds to two players, three rounds to three players and two rounds to four players. Some casinos carry this rule to the extreme and only deal one round to five or more players.
For example, under Rule of 6, with 2 players or 2 total spots being played, you should get 4 rounds; 6 - 2 = 4.
Except when using certain advanced techniques, single deck is playable with more than one other player only if Rule of 7 is in use. Even with Rule of 7, single deck is generally not worth playing with more than two other players at the table.
Under Rule of 6, single deck is only worth playing if heads-up playing two spots, or with one other player playing only one spot each. These conditions should yield four rounds.
You and two other players getting only three rounds is usually not worth your time, again except if you are using certain advanced techniques, which from the nature of your post, I assume you are not using.
Rule of 5 should be laughed at, not played. Paranoid casinos that use Rule of 5 (or Rule of 6) are shooting themselves in the foot. Such poorly-managed casinos reduce their hands per hour, and therefore their hourly win rate, far more than they would lose to skillful players if they offered a decent game.
The vast majority of casinos and dealers in the Reno area use Rule of 7. In Las Vegas, Rule of 6 and Rule of 5 are far more common.