Next release will be lots better. ;-)So after some testing I came to the conclusion that 839 and 764MHz on GPU in my personal use case scenario are unfortunately a hit or miss. Doesn't matter what voltage I assign to it, it will eventually just force reboot at some point or another, in some cases (not all of them, but most). Basically the GPU is capable of handling 764 and 839MHz but Samsung just didn't put in the hardware to handle it for long periods of time (unless somebody has got the luck to have an incredibly high ASV G71). Well, 683MHz is still a 25% overclock.
Just plug the original AFC charger or use any other USB charger that can supply at least 3 A @ 5 V or 1,67 A @ 9 V, then enable battery idle in A2N app and that's it ! There is no longer needed to set current @ max value since it's done automatically, (I'd patched that in some older release)
PS: max battery charging temp should be at least @ 40°C to avoid power drop.