For the money, I'd get it. However, the ammount of HP isn't what you should be looking at. You should be worried about the change in the HP and TQ curves. With the GT-40, you'll likely change your peak from about 5400 to around 5300 or lower.
I hope that came out the way I wanted it to sound. Sometimes I take a valid point and turn it to mush.

Anyway, hope I've helped. Later.
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"Is that a Cobra?"
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