Hi Rob,
probably you haven't seen it, but I have written a short assessment in an other thread.
I quote what I've written about it:
"A friend of mine has already used RPX in 35mm and compared to the Kentmere films (developed with the same times). I have seen the results: Same look, no significant differences.
So, nice quality films at ridicolous low prices. But with a different look compared to APX."
If you are interested in the RPX 400, just try it. It is available.
If you are looking for an APX 400 replacement, compare it to your APX 400 results.
Whether the soon coming Adox Pan 400 will be a replacement for the old APX 400......most probably the Adox will be different, at least in some characteristics.
Mirko from Adox has said that the Adox will be improved, with finer grain, true ISO 400 speed and anti-halation layer.
Cheers, Jan