With about 90 apps installed, of which BBM, WhatsApp, Vonage, LBE Security Master, Greenify, CSipSimple, Google+ and KeepScreenOn run all the time in addition to the usual stuff like TW, Messaging, GMS that runs with Android, My RAM usage with MK4 is 784MB. I don't find any lag in TW or in any of the games I play (except Ingress, of course - but that is an app issue).
I of course have rooted, disabled a bunch of stuff from loading automatically at boot, and frozen Sammy crap that I don't want or use. And no Knox.
XDA App is working perfectly fine, deep sleep seems to pretty good - lost 1% overnight after 2 recharge cycles. Auto Brightness is cranky at times - sometime stuck at lowest or brightest - but returns back to sanity after a display off-on.
Overall there is nothing new or extraordinary in the MK4 version from what we have seen in the leaks - except of course the knox status in the bootloader (I didnt care about it as am out of warranty anyways).
Haven't tried the stock browser with quick controls+full screen though, I rely on Chrome...
Xposed Framework with Wanam's module, per app dpi setting, message notification to toast, and then some more - all works great.
Samsung Galaxy Note II (GT-N7100) | HW Ver: MP 1.300
Baseband: N7100DDEMJ9 | Build: JSS15J.N7100XXUEMK4 | Recovery: TWRP 220.127.116.11
HTC HD2 (TMOUS) | Radio: 18.104.22.168 | HSPL: 3.03
cLK 22.214.171.124 | CWM 126.96.36.199 B8 Touch
No Sound issue with BT - Fixed!
Custom Autobrightness Levels with Flashing LEDs - Fixed!
Native Mount DataOnEXT with DalvikOnNAND
HP Touchpad 16GB
Moboot 0.3.5 | CWM 188.8.131.52
WebOS 3.0.5 | CyanogenMod CM9 (Nightly)