Take a gander here:
All-Star Sports Equipment
Also here:
All-Star: System 7 Hollow Steel vs. Titanium - Umpire-Empire
and,
System7 Allstar vs.UNDER ARMOUR SOLID PRO HEAD GEAR HELMET - Umpire-Empire
For me, I would get the 4000TI. the Sl seems like a good choice too, but I swear by my MVP2000, and I got the TI version in that model. I have no way to know if your data about the 2500 is right, but even if it isn't, I'd go with the best one I could purchase, and it ain't the 2500.
I'm back to a traditional mask now though I still use the HSM at times. there have to be others here with more insight than I do, esp, those who use the Shock.
That's my .02