I just wish there was some limit on the card that stopped it going over 2100mhz
Overclocking hasn't been worth it on these cards since the 10 series. Nvidia broke it for more casual users with the Gpu Boost algorithm.
It'll make its own adjustments regardless of yours, so that 170mhz OC was never really stable to begin with - and you've no real way to prove it, because it can't be sustained in everything.
The hotter the core runs, Gpu Boost will yield shorter and lower boost bins.
The more frequently it runs into the board power limit - also worse boost bins.
Overclocking increases thermals and the frequency of running into power limits. Gpu Boost doesn't like either too much.
Undervolting has been more effective on these cards.
Run Msi Afterburner. Unlink the Power and Temperature Limits - there's a paperclip like icon next to it depending on the skin being used.
Max out only the power limit, and click apply.
Play your games with Afterburner's own hardware monitor running. Make sure both Core Clock and Gpu Voltage are visible.
If Gpu Voltage is not visible, you can open it by going into Settings > General tab, checking 'Unlock voltage monitoring', and then go to the Monitoring tab, find and check Gpu Voltage. Then click Apply.
After a few minutes of playing, check Afterburner's hardware monitor for the MAX Core Clock and Gpu Voltage. Memorize, or write 'em down.
Please close the game, and open Afterburner's Curve Editor. Take the max gpu voltage you recorded, and subtract 0.05v from it. Find the voltage point in the Curve Editor that matches it, or is the closest match, and click on it.
Then use the up arrow key and raise the frequency back up to the max core clock the gpu touched. Lock it with the L key, and click Apply again.
Save the settings in one of the numbered profiles and lock them. Then click the reset key.
Done.
When you want to start up a game, open Afterburner, click the numbered profile it was saved at, and click apply. When you're done, click the reset button and close Afterburner.