Your DC and PA varies more than you realise, for example you won't be on rage pots / heroic pots all the time, you use them when needed, and PA torches too. Then there's buffs etc. and DC pots, and you'll sometimes change rings for clear/para etc.

For that reason there will never be a perfect answer for where the sweet spot is

You can calculate the relative value of a DC10 or PA1% socket though, I'll use the example you gave

1500 DC with 65% PA

That 1500 is calculated with 65% bonus already added, so divide by 1.65 to find the original DC before the PA bonus was applied, in this case it is 909. So if you add another 1% PA then it will add 1% of 909 which is 9, you'll get 1509 DC

Meanwhile if you add DC10, then that 10 is multiplied by the PA bonus, so it would be 10x1.65 = 16, so you'll get 1516 DC

Bear in mind that's only the max DC, I generally don't bother to calculate the lower value because everyone has max crit anyway so will always hit max. Only time you need to care about the lower value is in pvp where crit doesn't affect it the way it does with pve