I personally am a fan of using git to store the engine repo. It makes merging new engine releases easier. Then on the other side use perforce for your game content, but be sure that you’re excluding the git repo from perforce.
I actually go a step further and use git for all my code (engine and game) and perforce for just the game content. I think programmers tend to prefer the git workflow. I’ve found Derek’s website to have some good info on organizing perforce and git, it seems he has tried many combinations and ended up with the git + perforce solution.