It depends on your cars needs. I replaced my 2G with a 3G in my 90 GT Vert because the 2g would hang up and cause the engine to stumble. I got the 3g out of a Sable with a 3.8L. I had to use the stock wires since the alt i got has its lug near the bottom of the bracket after installed. I was wondering if I could rotate the back of the housing but I was pressed to get the car running.
To cut to the short is the demands on my charging system is stock thus the stock wires will be enough but if I were to upgrade to an electric fan, large amp and so on I would upgrade to a 4 or 0 ga wire.
BTW back to the fuse thing I think I have a 150 not 200 as I mentioned before. I know on my 93 the peak pull of the fan I have is at 100 amps so this fuse will be ok..