According to PE in that other thread, the Ilford is "about 25" but it will depend of course on the spectrum present in the scene. In my experience, Kentmere VC Select (and Fineprint FB) is about 1 stop faster than Ilford, so you probably get ISO50. Not sure if PE's testing involved preflashing but if it didn't, you might reach ISO100. Maybe. Note that there are a whole bunch of others in that thread saying "no, it's between 3 and 10".
Why don't you try it out with some bracketing?