Cpu runs hotter than gpu and I generally tend to put cpu before gpu in a loop to maximise cpu cooling. 70deg for 1.2vcore is pretty high imo.
You've also got pump/res after rad and before gpu. Pumps create heat so your layout isn't as efficient as it could be.
Think about changing it to pump/res-rad-cpu-gpu-pump/res.
Adding more rad surface area will help but as you don't have any temp issues with current setup I'd say you'd be wasting your money.
If you're looking to oc further though and add more volts then it would be beneficial.
Pump/res-140-cpu-420-gpu-pump/res.
No, loop order doesn't matter. This has been refuted many times over the years, temps always equalise in a loop in a relatively short period of time. Scientifically speaking the theory may suggest a minuscule difference, but it is so negligible that it makes no difference in real world terms.
Of all the things you can do to configure a loop, the order is going to have the least impact of anything, and in fact will have hardly any. Obviously pump needs to go below res, and the flow needs to be correct, but that's all that matters. Fan choice, fan speeds, rads, even coolant choice will all have a far bigger impact on temps than its order. I've seen people tear loops apart and change the order of everything, chasing better temps, and it always ends up the same or within a fraction of a degree (which is well within margin of error anyway).