Hi Rick.
You should also throw the LS5 MkIII in the mix. To alot of people's ears, mine including, The LS5 MkIII betters the REF1 and although I haven't as yet heard the LS25 MkII, imagine it may be better also.
Prior to the introduction of the REF 1, The LS5 MkII was ARC's top of the line preamp. From what I have read, ARC introduced the MkIII version in response to an outcry by those how had recently bought new Mk II's which ARC simply abandoned to bring the REF 1 to market.
The MkIII has the same circuit boards as the REF1 but with a beefier power supply. The LS5 MkIII just sounds more musical versus the more analytical sound of the REF 1. The LS5 series has the magical midrange sound of ARC versus the current house sound.
Anyway, just a thought. Good Luck, Mike.