JBL/Infinity(same company really) both claim the speakers to work with factory setups.I had a set of infinity two ohm 4x6's in my cavalier off of my pioneer head unit and had no problems. That 2 ohm rating is only a "nominal" rating. Basically the only time those speakers are going to be at two ohms is when they aren't being used.other than that the resistance is almost always much higher. I wouldn't be afraid to try it out personally.
the 2.x ohm rating is to make the final ohm rating with the speaker and wire an actual 4ohm rating. Where typically your 4ohm speaker has 4ohms resistance in itself, you add wire- and tada.. your getting closer to 5 (not much closer, maybe 4.1-4.3). So, when they say you'll get more power from your stock amp, you will- sort of. You'll actually be getting closer to the true 4ohm rating.
So figure 2.4 ohm speaker (i think thats close to their rating, and yes that's nominal- you're prolly closer to 3.5) + 15ft of wire = 3.5-4 ohms
big differences? Most likely no, atleast to an untrained ear.