The more relaxed you are the better in my opinion.
I used to have this philosophy on how to learn to drive fast that I applied with pretty good success. It went like this drive only as fast as you can be relaxed and still have enough focus to think about something else while doing it. Over time I found this would make you a better racer because you were relaxed at the limit of the car while everyone else was just hanging on trying to drive at 110% of their capabilities. One other part of this is you can see what you're doing well and where you need to improve because you're not hanging on for dear life. You won't be the fastest at first but you're playing the long game and you will be fastest in the long run. This of course means being relaxed.
On the point of real life verses sim if your driving tensed up in real life you might want to look at your seating position and if you are pushing or pulling on the wheel. Focus on pushing the wheel verses pulling and that will help you relax more also. When I drive any car in real life I'm relaxed even at it's limit because I set my seat properly so I'm not having to brace myself through a corner. Anyways if you need more specifics on this feel free to ask. SNAIL on!!
P.S. Congrats @
kcheeb