993 valve springs in 964 head?

[txhokie4life]

I bent some exhaust valves on my track car and while I was in there
I had some 993 valve springs installed that measured 20% stiffer.

They fit nicely so we decided to use them.

I don't plan on messing with the rev limiter but, I'm curious to know
how many RPMs of guard band did I buy myself.
So what does a 20% stiffer spring buy you
all else longblock wise being a stock 964 engine.

The engine has ITBs, fuel injection, and fabspeed headers with a Motec ECU.
Original 3.8 engine was pushing 400HP -- so the 964 setup has plenty
of external bandwidth.

I could have purchased various racing springs -- but we were tight on time
to get it put back together and I already had some 993 valve springs
that came from the original race engine that was in the car.

thanks,

Mike