i also think to change from my rn3 to rn4... if not so worth it i may just stop think.

so, actually , what good about rn4 over rn3 ?

I hope this is correct,

Note 4 - SD625 (14nm, Global) or MTK Helio X20 (20nm, China)

SD625 more power efficient and less heat but MTK processing more powerful and claims to be efficient as well.
Note 4X for here is using SD435 (28nm) less powerful than both above.

Note 4A is using SD425 (28nm), less powerful than SD435.

Xiaomi did a trade off to pair SD625 into Note 4 with newer design and spec in getting costlier SD650 but older tech in Note 3.

See if the future Note 5 will pair with SD660 but the price is going to be near to 1K mark, time will tell.