Digital BW, The Print

FYI here are some results of applying a straight 50% glop to various papers.
I took the measurements while doing some colour profiling using an Eye One
and the i1 TC 9.1B RGB Testchart.  I started by recording measurements of
patch 17A only to later realise it was not the darkest patch!  I
subsequently also measured patch 1A.  I also measured the impact on paper
white which was noticeable much more so than with coatings of 15% and 20%.
(Lab readings) There are a few gaps but it still might be helpful.

Epson Premium Luster:

Paper white pre glop    96.1  -0.4  -4.1
Paper white post glop   94.2  -0.7  -3.7
Patch 17A pre glop       6.6
Patch 17A post glop      4.2  -3.5   1.1
Patch 1A pre glop
Patch 1A post glop       2.5   0.2  -0.2

Ilford Smooth Pearl

Paper white pre glop    96.6   0.2  -5.8
Paper white post glop   94.8  -0.3  -5.4
Patch 17A pre glop 
Patch 17A post glop     4.1   -3.4   1.0
Patch 1A pre glop
Patch 1A post glop      2.5   0.2   -0.3

EPSG

Paper white pre glop    95.1  -0.6  -3.9
Paper white post glop   94.8  -0.8  -3.4
Patch 17A pre glop       6.2  -3.6   0.1
Patch 17A post glop      4.2  -3.3   1.0
Patch 1A pre glop        4.3   0.2  -1.4
Patch 1A post glop       2.6   0.3  -0.3