As a FCPX user on a MAC I do though wonder if Premiere would offer more fine and deep control?
I have no FCPX experience whatsoever. I can tell you that with Premier Pro it's very easy to zoom in on a timeline to see individual frames, and effects can be animated using keyframes. By "animated" I mean that you can tell Premiere to vary how effects are applied over any number of frames.
For example, let's say that you have some footage that you shot using Auto White Balance, and the camera decided to shift the colour balance halfway through the clip. Premier Pro has "fast" and "three-way" (shadow/midrange/highlight) color corrector effects that you can apply to the clip that let you control the colour corrections, including hue, tint, whitepoint, blackpoint, gamma, saturation, etc. All of these controls can be set using sliders or by direct entry of numeric values for precise control.
If your clip is 5 seconds long and the white balance starts to shift at the 2-second mark and completes it's shift at the 3-second mark, then you can set keyframes at those two points and specify all of the necessary color correction effect settings for both keyframes so that the colour matches at the 2- and 3-second marks. And you can control the rate of change of those settings between the two keyframes using linear extrapolation, bezier curves, etc. If necessary, you can add additional intermediate keyframes to exercise more precise control.
When you combine this animation capability with Premiere's myriad effects and layer masking capabilities, it makes for a tremendously powerful platform.