I can tell that the WiFi mod. made a huge difference. Originally I replaced the card in the controller only and tried that. It made an undetectable amount of difference. OTOH I did not expect that it would make any difference but since it was easy to try, I did! In theory it would allow you to get your signal out further but would do nothing for getting a signal back from the craft to the controller.
I then replaced the Wifi card in the Solo and that is when I started getting better range.
I have two Solos, this one that has everything replaced (HDMI cable, GPS, WiFi cards) and a stock one that has nothing replaced. I can fly the one with the replaced Wifi using the stock antennas further out than I want or need, right to the edge of what I can see (which is what I did out over the pond) and have excellent signal. Last week I went back to that same pond with the non-modified Solo but was using the Alfa antennas on the controller. I did not go quite as far (I only went 2200 feet) because the signal was dropping into the red.
It had been my plan to do multiple flights while I was there, using the unmodified Solo while trying different antennas (stock, the Alfa, and a Rexuav) but it was so cold my fingers talked me out of it after that one flight. Plus this thing intermittently refuses to fly due to "Level Calibration" errors (and it won't do the calibrate .. argh).