I currently have the Sony ECM-908C which I have carried over to use on my Panasonic DVC30. The specs for this mic can be seen here:

http://www.bhphotovideo.com/bnh/controller/home?O=productlist&A=details&Q=&sku=174982&is=REG&addedTroughType=search

I normally film driving events where I film cars driving by the race circuit or at the local autocross events. Autocrossing normally take place in a large parking lot with pilons setup everywhere and you drive as quickly as possible around the course.

My question is, is using the Sony stereo condensor mic more suitable than using an Audio Technica AT897 or the Rodge NTG-2? I know these two are more for dialogue, but are they powerful enough to capture the sounds of cars driving around from a distance? The parking lot I film at is just off a highway, so sometimes you may hear the highway ambience.

I'm trying to justify if I should spend the money of one of those two mics in hopes of improving the sound quality.

Do you have a way to input XLR mics into your camera?
Is stereo sound important to you or are you trying to get better isolation with a mono directional mic?
I think that spec on the B&H page for the signal to noise ratio is wrong, so don't let that necessarily sway you when comparing specs of other mics.