Thanks everyone for the info.  According to this article, for which I only have access to the abstract, RVX-297 is has greater selectivity for BD2 than does RVX-208:

https://pubs.rsc.org/en/content/articlelanding/2017/cp/c7cp04608a/unauth#!divAbstract

Supporting this is the reported 20-fold greater affinity for BD2 of RVX-208 (in the Picaud et al. reference that Bear linked) and the following statement in the Jahagirdar et al paper that I linked:

RVX-297 is a novel, orally bioavailable BETi that has a 47- to 58-fold greater affinity for BD2 than for BD1 in the BET family of proteins (Kharenko et al., 2016).  

The greater BD2 affinity of RVX-297 may have been a factor in its perceived utility in autoimmune indidcations.  The Jahagirdar paper also indicates that RVX-297 is orally bioactive as pointed out by Fouremm.

Of course, Bear is correct in that RVX-297 may not now be considered the best candidate for development as an epigenetic molecule for treatment of autoimmune disease - my interest is more in knowing the criteria being used to establish the best candidate than in knowing the current (preclinical) candidate.

Thanks again everyone - this board forum is a great source of ideas and info...

Jupe