Gel,
To be honest, you will never be satisfied with your tweaking - simply because you will always wonder if you are experiencing the best performance from your TV. One person will say this and another person will say something else.
Why agonise yourself over this? It will never end!
Put your heart and mind to rest by getting a professional ISF calibration done. You've got a brand spanking new TV that you've paid quite a few quids for, so don't you think this TV and you deserve this?
You want your TV to deliver the best possible performance in your own living room, so what anyone else is going to tell you is going to mean diddly squat!
Nick's house/showroom is not your house!
Ronald