Hi Harry,
First thing to notice was the poly difference between your initial work model and your final textured model.
Your first work model is actually 4885 poly's which is 9775 tri's, your textured and I presume further along model is 7041 poly's which is 14,049 tri's.
Most of this increase was in the wheels and I thought looking at these the originals weren't too blocky and square for a game model, may have appeared to be before you textured them
I got this down to 2724 poly's, 5325 tri's and without losing any of the edge flow of your model, I personally would take this a bit further but since it means starting to lose a little of your detail I reckon this would be a personal decision as to where you want to lose it so will let you decide for yourself. You could look at taking all the loops from the wheel arch and welding them into a single vert at the top of the chassis for instance though this will mean reworking your uv mapping.All the same it is in fact an acceptable high quality model for most game engines as it is.
Car on left 2724 poly's, 5325 tri's. Car on right 7041 poly's, 14,049 tri's.
Losing more wont hurt too much and the player wont notice these things at all as they won't stop to look over a prop and criticize, they should be too busy trying not to die so you can get away with a lot in game modeling. It's down to the texture mostly and once you throw a normal and spec map on it it will make a big difference.
A lot also depends on how it's to be used, you may never have the hood open for example and could lose all faces never going to be seen from both the hood and areas of chassis around it. You would be surprised how much you can lose this way
If it's not seen close up you could remove interior, wing mirrors,trims and so on, use a textured plane for the grill, might be worth using a small portion of your uv to do this for LOD if your going to use it.
You are doing it the right way by concentrating on getting it done then reducing where you can with a model like this..
