Hello All,
 
Would it be worth it to go from rsair HX1000 to AX1200?

If you are doing it just to do it I wouldn't, if your believe you current PSU may be dying or you need a 1200W PSU for other upgrades in the near future then go for it.  But if not then why spend the money?, you won't gain anything from the extra power.

PSU's have changed a lot since the HX1000. Back then, they were one of the only companies that were putting out legit specs. Now we have almost underrated PSU's. The rule of thumb used to be to shoot high and try to get something in the 50% load range to be safe. Because something like a HX1000 at 100% load would see capacitor ripple levels of 70mV or more and you will see it go up and up the longer it is around those ranges. Once it gets around 100mV after a few months of heavy use, it finally gives out. Most capacitors back then were rated for 120mV max load.

New platinum certified units run around 20mV under full load and they are rated for 150mV max load... so they last a lot longer. Because the more ripple means more heat and more heat equals faster degradation.

You should go with a AX860i.