@petkow
I have actually given away my Zopo C2 recently due to its very bad Wifi and GPS sensitivity about which I reported a while back on another forum:
http://forum.zopomobileshop.com/thread-1314-1-1.html (note
this post showing internal photos)
Though my device probably showed exceptionally bad performance you should be aware that besides serial dispersion resulting from wide quality tolerances at Zopo they use quite primitive monopole antennae for Wifi, GPS and BT instead of sophisticated duopole ones. You will not necessarily need to wait 5 minutes to acquire a satfix under a clear obstacle-free sky like I had to, but expect a Zopo to underperform quality brands. Further shortcomings of Zopo are that there's no 5GHz Wifi support and so far none of their phones supports GLONASS which could dramatically improve TTFF as well as accuracy.
In any case you should better order your device from a seller in your country so you can return it hassle-free, should you experience similar issues.
Regarding the ZP998 another advantage over the ZP980/C2 is that it supports UMTS on 900/1900/2100MHz, while the ZP990/C2 comes with the rather useless 850/2100MHz combination (at least for Europeans). Though I doubt that the ZP998 actually supports 3G for both SIM cards simultaneously, as you say. Instead it would rather have the ability to assign the 3G-capable radio module to any of the SIMs from the menu like I described it in post #9 of this thread.