4 gage is fine, thats what Im usin! And yes, there is a differance between runing the ground through the car VS runing it from the battery! Whoever told you to run your ground from the battery needs to get SLAPED HARD! See I have already been down this road, I ended up blowing an amp and 2 subs What happens is that since you have it grounded to the battery terminal and not to the car, it is actualy NOT grounded! The car works like a huge cable right? Well lets think of it more like a sponge for DC current. Now even if you have a wire goin from the batterie to the frame and the wire runnin to your amp(s) EXC, you are still not grounded (well not the amps/subs exc) Because the DC current is goin ONE way! It doesent travel back to the frame to make sure your amp(s) EXC dont get fried! Hell no, it goes wherever the least resistance is.... Therefor iether the current will go straight to the amp(s) ungrounded, or into the car frame.... Its hard to explane, but I hope that you can get the point