A good set of tires, an LSD, and a tranny that can keep up can do wonders for a FWD launch, but you'll still spin out. That goes the same with a RWD. A FWD, RWD, AWD will spin tires with enough power or poor set of tires or both. It's just that AWD has better control of it.
As for drivetrain loss, yeah, that's an added 10%. Nothing a better tune or bigger turbo can't overcome though. You won't see that loss unless you go side by side with a FWD car with the same motor, a GSX vs. a GS-T for example. But don't think that the GS-T will just fly away from the GSX, it's a gradual grandma pace. 10% is a lot with stock power, but barely noticable with higher HP. Depending on the setup and tune, the AWD car may have more TQ over the FWD or vice versa, but the FWD may have more HP. It's the TQ that will push you through the wind resistance and push the car forward and past the other.
The AWD system in my car is all mechanical. The pro to that is that the computer won't brake on me to control traction loss. The con to it is that it's fractions of a second slower to react over the electronic counterparts. I really could care less about the complexity of the newer AWD systems because if it's on an icy surface...it's going to slide, I don't care how advanced that system is. All that advanced technology is for is to replace the human thought so that you can talk on your cell while driving in snow or wet roads while taking a tight corner at higher speeds, period.
Just like the carburator vs. fuel injection. There's a human control over computer control significance with that old issue and that goes the same with the mechanical AWD controls vs. electronic AWD controls.

Ok, back to school work

 

i dont know what i want to do either stay with the 2.5L and just rebuild the engine or start from scratch with awd.... it is kinda pricy though for a stock AWD... not sure yet but i do deffinatly understand the concept of four wheels spinnin instead of one or even two is much better for launches.... but isnt that why you are supposed to heat the tires up before your launch so they stick anyways.... hmm i guess that is what this whole topic is about tryin to figure out what would suit me better... OH YEAH what is the biggest mopar or mitsubishi engine that can fit under the hood of the avenger... is the 3.0 bad venge about as big as it gets or is there bigger.. and what would it risk with it being front wheel drive, also is there a way to convert it to RWD or no? im hoping to find a beater here soon so i can park the venger over the winter and start to tare it apart...