Believe it or not, you have another option. It's a bit extreme, but a few people have replaced the motor all together! They've put in V-8s. There's one Crossfire with a Hemi 5.7 in it. And two with Mercedes E55 motors. And I think there are three with Mercedes 55 AMG (supercharged) motors in them.

Another option, that might be cheaper, is to buy one of the SRT-6 motors from the V-8 swap guys (Paul and Rudy) and have them put that motor in yours!