someone correct me if i'm wrong, but the 5150 has a remote resevoir, which provides a large capacity to reduce heat buildup, and thus reduces shock-fade as compared to the 5125. For what its worth, if you aren't doing any high-speed desert stuff or whoops, then probably no need for it, as you won't build up near as much heat just crawling or on the street.
is that about right vetteboy?
edit: where have you guys found the 5125 series for sale online. everywhere i've found only has 5100 series or 5150, but no 5125