The break down.
The current 08 Challenger sits on the LX platform. 6.1L 425HP. DC did this because they already had a proven platform to give the consumer limited production car while R&D was being done on the 6 speed, new rearend (LSD type) and larger powerplant (for SRT8 model).
The 09 model that will be available late Aug or Sep 08 will introduce the 6 speed, new color schemes, V6 and R/T lines.
The SRT8 for 09 with a larger power plant is still a speculation and nothing confirmed. However, DC is currently offering 100 Drag Car options for the 09 model. This may be where the 510+ HP is coming from.
In any event, the Challenger IS the car of today and tomorrow. hehe At least until the Camaro is intro'd.
Hope that helps a little.
It is also rumored that DC is looking at a few Super Charger companies to add FI to their line.
And there are many reputable shops producing some very powerful 426 and 392 motors. The ones listed earlier (aside of Indy and the X??) I would shy away from. IMO