I am using HBH-GV435, it sound better, clearer and louder compare to my old HBH-608. But the buttons position is kinda odd. I am still getting use to it.
1. Ya the battery life of P990i is average, if there is any activity on your phone during midnight, exm: sms, mms, miss call, reminder and etc. The green lights will blink fast to gain your attention which will drain the battery even faster.
2. Some suggested that by using Tweak Peak (Disable the transition effect) and Swiss Manager/Pro will make P990i performance better. For my case, I have uninstall both applications because I had more problem when both applications installed.
I've found out a trick here, if you click the shortcut and calender icon (the most left icon when flip open) often, it will decrease the RAM amount available which leads to auto restart even if you have Swiss Manager/Pro installed. Avoid clicking the icon will make your phone performance much much more faster and stable.
3. Yes you are using Singapore Chinese enable set like mine here, the firmware is kinda old, the last update was back at mid of February.
These are some of my comments and experiences. Hope it helps !!