IComing from SL I switched 2 years ago to ML - was even with OSX 10.5 until 1 year ago on my MBP classic from 2012 ...
It just worked fine.
Switched about one year ago from there to 1o.11 and was very pleased about it.
about 2 or 3 months ago I switched again - now it is Sierra aka 10.12 - works fine and even more faster on my 2012 machine (though upgraded since years with fast Samsung SSD ´s and now 16 GB RAM).
IMHO 8 GB is enough RAM, never had Problems before upgrading to the max of 16 GB ( I did this just because RAM got very cheap, even Samsung). ElCapitan and Sierra handle RAM even more economically.
I would NEVER EVER recommend to switch to the newest OS before it gets really stable and usable - this is the case just before the next-after OS starts "traditionally" with all its bugs and problems. Would not even think about testing High Sierra now - BUT: ElCapitan and now also Sierra are really worth to go for it.
As you see, I used very old , but stable OSX-Versions for a long time (Don´t change a running system) - but I did not regret upgrading - I am very pleased with Sierra.
I was very careful: Using a 2 TB SSD in my MBPc, I created two "drives" of each 1 TB.
The old system rested on 1 bootable system. CCC helped me to copy the whole System onto the second virtual drive on the SSD (might take a night, depending on quantity of data) .
Then I upgraded the new Copy of the old system with the new OSX.
Since both (new and old systems) on the virtual disks are fully functional and bootable, there is zero risc for you and you can compare them and test the new one as long as you want to.
After my good experiences with 10.11 and 10.12 I can recommend to go for Sierra.
Go for it!
edit:
the newer Safari-Versions are much more secure and double as fast as the old ones.
And apple did really much for more security of their Software.