Ok so ran another test on Cinebench R23 how you asked, after starting the test, I immediately reset the timer. I took 2 screenshots in last 30 secs. First half of test was 3.99GHZ, then in middle it was 3.95GHz, last half of the test ran at 3.94GHz, reported in Task Manager.
3x Intake fans are Arctic P12 PWM PST
1x Exhaust fan is Corsair 120mm Air Guide fan
Should I do fan tuning as well? Say, at 90C, I think I should make the intake fans run above 1500 RPM and exhaust above 1000 RPM, no idea if Corsair fan will go above this.