Sorry about your GPSs. I suppose they are burned and don't work. Maybe just the 3.3V regulator in them, but a pain to buy and replace the regulator. 
By default, the ~5V input voltage is not connected to anything that can measure it so any proposed change to the GCS would have to take into account that for a default. The user could connect the standard way that the battery voltage is measured through the "sonar port", and view it as if it were the battery voltage, but I doubt that is useful enough for you to bother with, and I would not bother setting it up for my stuff. 
Some people even choose to use 6V to make their servos faster, etc. Many RC receivers can handle 10V or so by design. The original CC3D design was up to 15V IIRC, so running it on 7.5V is not breaking CC3D specification... Sorry.
No Cliff, fortunally it didnt hit me in such a annoying way. The naza gps just refused to work (on a putty which is directly attached) you can see data stream which goes over the serial line, but proably it talks nonsense and the revo isnt able to understand. When then input voltage goes back to normal, the naza gps again works fine. Now i own two working naza gps (a reason to build a bigger copter) , and after changing the racer board to my old one (electrically fine, but one socket was mechanically broken, but hot glue keeps the plug inside), everything turns back to normal.
Because the naza didnt work, but a ublox did, i assumed the gps was broken, at that time i didnt suspected the input voltage. But after the second naza showed the same problem it was clear that the problem must be somewere else. And that guide me to check the board voltage.
But interesting is the flashing pattern:
Voltage too high: solid red for about 20 seconds, then rapid red blinking.
Voltage normal: slow red blinking, with additional blue flashes as it finds satellites.
Udo