It's hard to say how it will respond as each R compound has slightly different widths for a given tyre size. Obviously the best way is to test but then you've forked out the bucks already.
As an aside, When looking at the R888s I was advised slightly away from them by some other circuit guys on here stating that they are in the same ball park grip wise as a KU36, which isn't even an proper Semi.
Can you use your contacts to get some cheap AO50s or RE55s? What are you currently using?
I'm in the process of shopping myself and might just grab another set of second hand RE55s as mine have been good.