Can't speak for the G7900, but I got the 7710.
My guess is that quality is the usual high g-shock-class for both of them.
A little search around and you'll probably notice that the 7710 has one of the better modules (apparently).
A few thoughts on the 7710
Pros (imo) - things I appreciate and use daily.
- weeknumber, day and date on normal clock-setting.
- stopwatch
- Countdown-timer (double)
- alarm (several types; daily, weekend, with snooze etc). Not loud but enough to wake me up in the morning

- automatic light (activated for up to 6 hours)
(Also with world-time... I don't use it though)
Cons:
- the light is only on for 1-1,5 secs. Only thing that bugs me!
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