Did anyone perform similar A/B testing of Fomaspeed?
Not with Ilford, but with some (by now, old) Adox MCP, and the purpose of the test was not so much to do a side-by-side paper comparison. I was mucking about with LEDs for VC B&W printing and this involved some step wedge work as well.
https://tinker.koraks.nl/photograph...e-leds-for-variable-contrast-black-and-white/
However, I can confirm that:
* Dmax of the Foma paper was slightly lower than Adox. The difference is measurable, and also visible in strong light. Under subdued light, the difference is minimal.
* The Foma paper does have a different tone to its blacks; it looks more purple/magenta compared to the more neutral black of Adox MCP, again under very strong illumination.
I've not used the 313 product but it's conceivable it has a slightly warmer base, perhaps? The measured Dmin on the Fomaspeed I tested is around 0.085; the Adox was very slightly higher around 0.095-0.100. Not a huge difference and Fomaspeed's white is a perfectly acceptable white indeed.
I did note interesting H/D curves on the Fomaspeed paper when exposed to pure green (550nm) light; however, the practical relevance of this is very limited since this is not a usual way of exposing the paper, as it gives something like a grade "00000" contrast (i.e. far lower than grade 00). In reality, you always expose with a little bit of blue as well so the curves blend better and the paper does become more linear in that case. Still, you may still see a bit of an odd 'bump' in the H/D curve of Fomaspeed at the lowest contrast grades. It's more linear at the higher grades.