Sorry I missed this.
Yes a stiffer rear bar allows for a quicker weight transfer forward when you lift. This allows the front tires to set quickly and increase the rear slip angle so the car will point towards the apex. Now you can begin to unwind the wheel and roll on the gas early, being at or near full throttle at the apex. This is the fastest way around a tight corner IMO.
A perfectly balanced Boxster likes to prescribe a nice constant radius arc in a corner. This is what we all want on those fast 3rd gear sweepers. By stiffening the rear just a bit we can alter that arc as needed for a quick turn-in on tighter corners and get the car pointed where we want it to go.
The devil is in the details and the "stiffer rear bar" works best on a car running 225/255 stagger. If you run square with a stiffer rear bar, the rear gets slap-happy and tends to step out at 85 mph on those fast sweepers. Been there, done that... and not doing that is better.
Getting the car balance right for your local tracks and your driving style is a process and is not the same for everyone. This is why dedicated race cars run adjustable sways so they can adapt to changing conditions and changing tire setups. For a dual purpose car running staggered setup, I like the M030 rear sway a lot to put the car where I want it to go without getting too extreme.
I see some guys doing their own setup and they put heavy springs and a very stiff rear sway on the car. Now the car skips like a stone on corner entry and they get a lot of wheel spin on corner exit. They can't understand why with all of their "upgrades" the car is turning slower laps. The answer is simple: Wheel spin is slow.
Happy hunting!