FWIW, the lady at the vape store told me that a 0.8 coil is recommended for combo XROS + Nic Salts (50/50 ratio). Haven’t tried it yet as I was too cheap to buy another pack of coils while I still have plenty od 0.4.
Last week, I had a pod leak (I was already using it for 3 weeks and I refilled it as usual- and it simply leaked
) and my vape was soaked with the liquid. 
I thought it was ruined as after cleaning it up, I changed the pod - and it clogged the pod again. It turned out that the liquid got into that little round spring-like mechanism and then it clogged one of the little holes in the new pod. So I tapped that mechanism with cotton sticks dipped in alcohol and left it all to dry. I used a toothpick wripped with a paper towel to clean the hole in the pod and also left it to dry.Not to waste nic salt, I‘ve put 70/50 liquid in a new pod to test the vape, and smoking that was not enjoyable at all compared to Nic Salt. Hard on the throat and no kick. Then I mixed it with nic salt and it was even worse taste.
Couldn’t wait for it to be used up so I switch back to pure Nic Salt.
In any case, a good news is that XROS PRO vape can be saved even if the pod leaks inside it. It’s tricky and a long process but is doable. One has to really clean it as the liquid will be everywhere, also in the air flow, which is difficult to clean.
I was looking at 3 and 4, because of the size, but I like the PRO as one can adjust the power more.