The Holden (GTO) and the Opel (Catera) have only one thing in common. The are both produced by GM. The Opel platform that gave us the rather boring Catera was a midsize FWD platform, not rated for more that 325 BHP. The Holden, however, is a RWD midsized platform that is rated for over 500 BHP. It is larger by over 9 inches in wheelbase and comes in 3 different sizable lengths. They build an El Camino-type version of this Down Under - called the Ute.
The Holden will only be used in the first year of production, as Pontiac gears up the new GP. The production will then shift stateside, in accordinance with an agreement with the UAW and be based on the GP, a la Monte Carlo and Impala. If the sales of these two coupes continue to climb, watch for a coupe (albeit a limited run) version of the Bonneville for the 50th anniversary run - most likely in GXP format only.