GXP pricing is on Edmunds.

Though the Pontiac (US) site still shows it under 'coming attractions' . . .

KBB site seems to have some 'issues'.

Official HP / TQ ratings:
“LS4 NEW! Engine, 5.3L 5300 V8 SFI (303 HP [226 kW] @ 5600 rpm, 323 lb.-ft. [438.0 N-m] @ 4400 rpm)” – from the GM Ordering Guide on line.

[Edit: The LS4 is all aluminum - and is reported to be essentially the same weight as the 260 / 280 S/C 3800 in the GTP. ]

My understanding is that production of units for customer sale began earlier this week.
- Ray
Ready for a test drive. Now.