[Rat3d ///M]

I hope this is a good place for this, and I can get some help. I am looking for people who are very familiar with GoPros and the differences between each model.

I currently have a GoPro Hero (the original). I have had it for maybe 4 years? Picked it up used and shot some sport bike and a few car videos with it (mostly sport bike related). I am looking to add a newer GoPro to it, to shoot some car videos.

Here is the setup I want to obtain:

1 GoPro mounted to the front windshield for a front view, 1 GoPro mounted to the back window facing the rear for a rear view, and an external microphone running outside to the back bumper to catch the exhaust sound. This setup would be used for the track. I also want something for filming other types of automotive videos, mainly of group drives/cruises, and other videos of the sort (with the camera mounted outside the car).

That said, I planned to use my current GoPro as my "rear view" camera, and muting the sound (since the original Hero has horrible sound). That would leave me needing another GoPro for the windshield, one which would need to have an external mic input. This GoPro would be used for capturing the sound of any videos I shoot (most likely using an external mic 100% of the time). Since the original Hero doesn't have an external mic input, another Hero is out of the question. That leaves me with the Hero 2, 3, 3+ or 4.

Now my specific questions are:

1. I understand the Hero 3 White Edition has the same 5mp sensor as the Hero, everything after the Hero all have external mic inputs, the newer GoPro's have fancy features, and everything starting with the Hero 2 was upgraded (with the exception of the White Edition) to an 11mp sensor. Other than that, I don't know anything about the newer GoPro's. So, for what I want to do, what GoPro do you recommend? I am afraid the Hero 3, 3+ and 4 just have more features over the Hero 2 that I will never use, but are otherwise basically the same camera. Is there any reason for me to spend the extra money on the Hero 4, or even the Hero 3/3+, or would the Hero 2 work just fine for me?

2. How about the quality of the external mic input on the Hero 2? Is it inferior compared to the newer GoPros? I want to make sure whatever external mic I plug into it will be able to relay good sound quality to the camera. If the external mic input on the Hero 2 is garbage, that is a good reason for me to consider the Hero 3 or 4.

Any advice you guys can give is appreciated. I know this was a long post, just trying to get an idea of whether the Hero 2 will work for me and I can save a few bucks, or if I should absolutely (for whatever reason) go for the Hero 3 or 4.