I disagree. There is a huge different between 6 and 8 ps. Regardless of your class, 2 ps is still worth 16% more damage. It will still take you 16% less hits to kill even with a torch. There is also a damage bonus for the 6 more strength, this is absolute, so 1h benefits just as much from this as 2h. Especially because the low base damage from 1h, having high ps is important to minimize the chances of glancing.
The mentioned held attacks and speed bonuses will stack with your ps. So doing a perfectly maneuvered held hit will get even more bonus with more powerstrike. Still the increased speed bonus from having more athlethics does not at all make up for less powerstrike, it is not that significant.
Real world maths comin' at ya!
Let's assume you have an opponent with 21 str, 7 IF and 55 body armor. That gives him 70 hp.
Now for the builds of the attacker.
Build 1 has 6 PS and 123 WPF.
Build 2 has 8 PS and 123 WPF.
The three weapons being used are a MW Italian Sword (33 cut), a MW broad 1-handed battle axe (38 cut) and a MW Military Hammer (31 blunt)
Not counting held attacks or speed bonus, it will take the guy with 8 PS 3-8 hits to kill your opponent with an italian sword. So, an average of 5.5 hits.
Not counting held attacks or speed bonus, it will take the guy with 6 PS 4-14 hits to kill your opponent with an italian sword. So, an average of 9 hits.
The damage for 6 ps here is probably more of a statistical fluke. The damage must have just hit a threshold with this combination of armor and hp. Following trends it should be closer to 6.5-8 hits on average.
Not counting held attacks or speed bonus, it will take the guy with 8 PS 3-5 hits to kill your opponent with a hammer. So, an average of 4 hits.
Not counting held attacks or speed bonus, it will take the guy with 6 PS 3-6 hits to kill your opponent with a hammer. So, an average of 4.5 hits.
Not counting held attacks or speed bonus, it will take the guy with 8 PS 3-6 hits to kill your opponent with an axe. So, an average of 4.5 hits.
Not counting held attacks or speed bonus, it will take the guy with 6 PS 3-8 hits to kill your opponent with a hammer. So, an average of 5.5 hits.
This also doesn't include damage bonus from movement. If you added that in, damage results would be even closer. The initial weapon damage and damage type is FAR more important than the amount of PS you're stacking ESPECIALLY for 1-handers. So, the amount of point investment you're putting in to pump you to 8 PS has a VERY small effect on damage. That is why I always say balanced builds are king. This also doesn't account for the fact that the build with lower PS probably has higher WPF, bringing damage values closer again.
With 2-handers and poles, you'll see a much larger difference with stacking str, but mostly only on cut weapons.
As an added point, if you can block decently you destroy people using a 6/33 spear build. Just sayin'.