after i flash with dxkp9 and cf-rooted, found out that the phone will restart once everytime i on it.. tat's weird only once! then after i swapped the sd card, kies say my phone is not connected in kies mode everytime i plugged the usb... =(

first thing i did was try the wifi driver code. Does not work. Saw some threads in xda about this even in xxkpn, there were claims that using static ip address can solve it so I'm waiting to go back home to try.

FWIW, at office I don't have this issue yet.

BTW 2.3.6 xxkpq is out

Yes, I did initially flash it to DXKF1, then upgrade to DXKB2, then to XXKPE, before to DXKP9 finally.  Result still the same. 

I had the phone working for 1 day after I update it from the stock DXKB2 straight to DXKP9 via KIES.  Then the Menu and Back became unresponsive from then onwards, only then I started using the ODIN3 to reflash it, but it's still not working. 

Class 4 is ok but it wont be enough for shooting HD vid. You can notice some startling during the recording (as it is saving as much data as possible per second, it could fill up the buffer, hence startles). Class 10 would give you more headroom and nearly zero lag/startle/glitch in you vid at least.

Furthermore, when u start to accumulate more vids+pics in your phone, speed is everything. Browsing is a little slow on Class 4. Class 10 would give you better browsing speed. This is what I see.
Plus, if you apps were moved to SD, it would load slightly faster for some apps.

class 10 will hav effect on video capturing....720p can be risky using slower cards

how much you bought it?