Hello,
I believe that thicker cylinderwalls are more stable, thus less suspectable to blow through the seal. But giving the studs more torque only stretches them more in my opinion.
I even think that there isn't much difference between 5mm or 6,5mm. The difference has to be bigger to be measurable or noticable on a N/A motor. It's a different story when you start to play with turbo's
Then it's nice if you have the 6,5mm thickness because you have enough thickness for an interlocking sealing ring.
Just my 0.2 cents.
Cheers,
Richard