You can max out at 4.1 if the chips good enough to do that while keeping below 1.40v
Trouble is the binning is all over the place because it's a new process.
I've seen people hitting 3.8ghz on 1.325v then need near 1.4v just to go 100mhz higher
Generally 3.8ghz 'comfortable' unless you happen to be very lucky
Comfortable meaning low 70's c
stress testing which is where I like to be personally.