My problem with mch and 2.40B are probably just an issue with my particular board, you may very well not have an issue with it or 2.50A. My nb is also water cooled and when I was still benching with 2.40B on the cold nights it would get even more sensitive to mch voltage. Do you know if the extreme has been moded yet? It has no LLC and apparently the vdroop is pretty substantial in unmoded form.