Just google GTX 1050Ti over-clocks and see what other people have gotten. No one can give you the safest peak because when it comes to over-clocking, everyone gets different settings that they can achieve.
For example:
1 guy can over-clock is FX-8350 all the way to 7.0GHz at just 1.5V's
but most people aren't able to over-clock the FX-8350 to even 6.0GHz..most being 1.5v's at 5.5Ghz usually.
The reason for this is because it's become what we have known as the silicon lottery. You either get an amazing card that can over-clock extremely well, or a card that does it normally, or a card that will do it very poorly with you barely able to achieve even 100+mhz clocks.