OK ,so the two Problems of Miuiv6 5.2.6 is *solved* →

1) Root Access →Flash this Zip ( http://d-h.st/2XQN) , even after this u face any problem, download SU from play store like I did...and now everything is going fine

2) Performance Mode → this isn't shown in ROM but reality is that it's hidden... Now how u unhide that... Idk but I used a trick to unhide that I.e. use ANTUTU BENCHMARK App tongue emoticon When you will run antutu benchmark first time... It will ask for you Balanced or Performance 
Select Performance and you're done ‪#‎Enjoy‬