Guys what would be better for performance and over all longevity for a 2005 Bonneville Gxp. 4.6 liter north star engine. Platinum or iridium spark plugs. I was thinking of going with Ngk iridium plug but don't know if they are any good for this particular motor. Thanks

I would look up the original equipment (likely iridiums) and go wtih those.

I know the plats tend to break down very quickly in the 3800 motors, based on a waste spark setup. If you have the same (I think you do) I'd stay away from plats.

I strictly use iridium.

used Bosch Platinum+4 in my 3.8L for over 200K mi, worked great improved fuel mileage and seat of the pants performance. Just recently switched to them in my GXP, been working just fine for the last 6K miles and seems to have improved fuel mileage slightly but to earlier to be conclusive.

OEM is Iridium. It lasts longer and fires better than platinum.

The OEM plug is generally going to be the best.
If there was a miracle plug that really improved mileage and performance, don't you think the car makers would have spent a couple extra bucks on them? Trust me, they would have easily spent $50/car to claim a 1mpg higher rating.
My OEM plugs are at 145,000 miles. I don't "think" my mileage has gone down much with these old plugs. (right now, I'm more concerned about that annoying vibration at 73mph.)