6s to 7, not much. But future proof it. It's like you said , rm500 difference unless you can't live without the headphone jack.

Get the 7 bro
6s battery life not good one

Specs wise there is a improvement in processor speed. Like myself, I upgraded from ip6+ to ip7 and I can tell you there is alot of difference in term of speed and worth the extra $$$ to fork out for it.
I personally use cables from Anker & Aukey, especially those with braided and high capacity cables. I have forsaken other brands as they are more sensitive and are not that lasting. Original cables are good but they tend to split at fittings, but not these braided cables by Anker. In fact they charge your phone faster too with the right charger. I myself use the 12Watt Ipad charger + Anker Nylon braided cables to charge iPhone.

Day to day use, i doubt you'll see much performance differences between 6s and 7.

I think if you wana compare, you'll have to consider the incremental stuff like the camera enhancements, water proofings are justifiable for the additional costs.