ARC Ref mark2 vc Supratek Chardonnay

I'm looking to upgrade my ARC LS15 and the two pre's I have narrowed the field down to are the Ref mark2 and the Supratek.I know there are a lot of happy Supratek owners on this site( I have posted in the asylum but get the feeling Supratek owners frequent here.) Have any of you directly compared these two pre's?I have talked to a couple of Supratek owners who are delighted. Would the chardonnay be a sideways step or a forwards one?I don't have a bias either way.I know thre is a ref3 on the way.
Accompanying gear- ARC CD3 ( balanced), Plinius SA100 ( soon to be Sa ref) and Shahinians.Music taste classical and jazz.
Thanks in advance,
Kevin