A buddy of mine was kind enough to ride along with me and filmed a run from second gear on the highway. We were on a very sparse stretch with little traffic so I decided to see what my car could do.
Using the top speeds for each gear (from an old issue of Road & Track) I have calculated a couple times using the video. Keep in mind this is far from scientific as I am just watching the timing on the video and listening for my shift on the video. I have no idea how accurate these are and without proper instrumentation theres no telling.
Third gear to Fourth gear (64-91mph) : 3.5 seconds
Fourth gear to Fifth gear (91-128mph) : 8 seconds
I'm using the chart from a stock wheel/tire WRX, but I'm running 17inc rims. So I'm not sure how far off the top speeds for each gear would be.
I have the video if someone wants to host it.