How about you make 2 different saves and do both? I did.
Personally, it has no real impact either way. I chose to continue the game after killing Playboy X.
Kill Playboy X and you get his pad (always useful to have a safehouse in the top part of the island), a secret outfit (Claude's from GTA 3) and if you befriend Dwayne enough you can call on a pair of his boys to go into battle with you. Useful cannon fodder as the AI's a bit crap.
Useful yes, important to the game? Not really, plus if you befriend Dwayne he's ALWAYS MOANING like a whiny emo bitch - I wished I capped him after all.
In fact, I'd strongly suggest killing Playboy X to get his pad - it's PERFECT for taking on the police and army for the One Man Army achievement.
Plenty of space on the balcony to cause carnage right up to 3 stars without reprisal, and outside the cops storm the building in front of you giving you perfect opportunity to take them out from behind the walls on your roof.
Even the gunships can't get you properly, but a quick dive back into the pad gives you some breathing space to ready the rocket launcher!