You also need TA, specifically the carbonate component of TA (so subtract one-third of the CYA level from TA) to saturate the water with calcium carbonate to prevent pitting of pool plaster.
The Pool Calculator does this calculation for you including the adjustment to TA for CYA.
You will notice that the higher salt levels create a more corrosive saturation index. At a pH of 7.5, TA of 70 ppm, CYA of 80 ppm, CH of 300 ppm, TDS of 3200 ppm (for salt level near 3000 ppm), temp of 85F, this results in a saturation index of almost -0.5. So in this scenario, it would be better to keep the pH closer to 7.7 to 7.8 which would also help slow down the rate of rise in pH (lower TA and higher pH slow down this rate) and would have an index of -0.3 to -0.2 which is fine in an SWG pool.
The above isn't a huge deal, but if you keep pushing it and lower TA to 50 ppm, then at a pH of 7.5 the index is down below -0.7. This is why I generally give a lower limit for TA of 70-80 ppm in an SWG pool when the CYA is 60-80 ppm. In a non-SWG pool with lower salt and CYA levels, one can go as low as a TA of 50 ppm if they target a pH of 7.7 though this is a pretty extreme scenario and most are fine at 70-80 ppm TA with 7.5 or so pH. Again, in both situations, this assumes that the tendency is for the pH to rise; in a pool using an acidic source of chlorine such as Trichlor, the TA should be much higher such as 100-140 ppm to provide sufficient buffering against the strong acidity.
If you still find the pH to be rising more than you'd like at the lower TA level of 70 ppm and at a higher pH level of 7.7, then you might consider adding Borates to the pool as described
here. Not everyone finds borates to help with rising pH, but many do.
Richard