where u brought and how much?

Wow, RM980   At Directd only RM960 for Black Color  / RM929 for Silver

    BTW u did not brought from Directd or 7 Mobile right?

I don't think so benchmark mi3 win. But touch wiz have huge delay when bringing up recent app list and animation when switching app is not smooth.

anyone has updated your dev rom 4.6.6?

MIUI ROM 4.6.6 Full Changelog
More: http://en.miui.com/thread-23486-1-1.html
[System]
Fix - Slow charging speed (Mi3 WCDMA/CDMA) (6-5)
Fix - Sometimes couldn't open WLAN after booting (Mi3 WCDMA/CDMA) (6-5)
Fix - Sometimes couldn't connect to any WiFi router without rebooting (Mi3 WCDMA/CDMA) (6-5)
Fix - Recorder couldn't adjust volume on speaker (Mi3 WCDMA/CDMA) (6-5)
Fix - OTG couldn't write in (Mi3 WCDMA/CDMA) (6-5)
[Messaging]
Optimization - Optimized UI of Notification messages. Support viewing messages by types by pulling down (6-4)
[Camera]
Optimization - It blurred when long pressing to take pictures (Mi3 WCDMA/CDMA) (6-5)
[Gallery]
New - Press the blank area to add pictures when Cloud images page is empty (6-4)
New - Support editing pictures in cloud albums (6-4)
New - Support pinching to return to image list when viewing pictures in full screen (6-4)
[Mail]
Fix - Some POP accounts could not log in (6-3)
Fix - ZIP attachments did not automatically open after downloading (6-3)
Fix - Using 'Sort by' in searching results may cause FC (6-3)
Fix - Could not send mails by clicking the email address in contact details page (6-3)
[Browser]
Fix - Some webpages said password was not filled in after auto-fill (6-4)
Fix - Some webpages didn't zoom in/out by double press (6-4)
https://www.youtube.com/watch?v=WhG-EFEoSHc...3D-Brj4H9dQvYJA

No Bro,

if you already DEV ROM 4.5.30, just use the OTA to update it.

if you want to flash it from Stable ROM  to DEV rom,
use this link
http://en.miui.com/download-101.html#164

and follow the flashing guide please