I bought a new laptop, my old one was getting old so i bought a HP:

HP Envy 17-J011sp
Intel® Core™ i7-4700MQ Quad Core
12GB RAM
Nvidia® GeForce™ GT 740M (2 mb)
HD SATA 1 TB 5400 rpm
17" Full HD 1920x1080

I am very happy so far. I run games quite well.
17" screen is great (for a laptop), i have a big area to work.
Some games i can run at 1366x720 with ultra detail, some i can go to 1920x1080 medium/high detail
SKyrim as example i can play at 1920x1080 high detail
X rebirth even in 1366x720 is a bit slow, the game is very demanding...

Questions
1)
i think 8Gb of ram is more then enough for everything, i have 12... back in the days there was a rule, that RAM should be upgraded by multiples of 2... 2, 4, 8, 16.... 12 is in between 8-16 ... would i gain anything in upgrading to 16gb? Gaming only, i know that for edit video if would be better, but is not the case, the videos i do, 8GB is more then enough, but for gaming... can i gain anything, i think not.... but

2) The Hd is SATA 1 TB 5400 rpm. Would i gain anything (gaming) in change it for a faster HD? Loading times would be faster, but after loading, the frame rate would be the same i guess....