Maybe it is totally useless info, but my old PC also has similar issues, namely having very high ref value beside acceptable values in other places. It is a single core AMD 3500+ with a Geforce 6200, and as I remember its performance was better in the past. It is simply too slow for any shadowmapping scene made with game engines (but okay with some games), nearly throwed it out, but temporarily kept for music recording... I decided to make projects only for no so old machines.