(where you control each individual frame A/E/I/K/P)
I'm not familiar with the FCP6 Strobe effect so I'm not sure if that's what you're after.
There are two ways to do what you're looking for - a simple way, and a complex way. First, Motion has a Strobe filter (Library-Filters-Time-Strobe). Create a FCPX Effect, add Strobe to the source, publish Strobe Rate and Mix, and you're done. This unfortunately doesn't give you precise control over the frames, but by controlling rate you can get close.
If this doesn't give you enough control, the best option is to bring the footage into Motion and keyframe it manually. I'm not aware of a way to publish those keyframe controls to FCPX, unfortunately.