You won't get any additional power, but the lighter weight will make the engine RPMs climb faster. You can have a stock FW machined, but only so much because the integrity of the FW can become compromised if too much material is removed. I'd suggest looking into a lightweight, aftermarket FW. If you're going to pull the tranny apart, you might consider replacing the clutch and throwout bearing if needed.
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2005 s2000