In reply to Offwidth:
Sure. I'm not going to analyse the grid in detail other than to tell you that in physical difficulty it all looks ball park to me and I've got enough experience to feel sure of my opinion.
As a guidebook writer you might want to do something different to guide your (not necessarily experienced) customers into informed choices. I guess that's the idea behind the banding, just I've never even looked at it, let alone tried to apply it. And I am colour blind, so it would be a pain for someone like me to use if I were minded to. You might bear that in mind: somewhere towards 10% of guidebook users are likely to share that problem.
How hard something feels is likely to be part cultural and most relevant to the lower grades. By the time someone gets to be onsighting in the uppper 7s that's likely a savvy climber who knows their own mind anyway. As today's new climbers learn more on plastic and less on the Milestone Buttress in the rain, that basic trad competence is likely to be lower than when I started climbing, and consequently trad standards in general have gone backwards if anything. There aren't that many trad climbers wombling around the E4-5 range when there used to be more, cos we were all trad climbers way back when. Or so I believe, anyway.
So trad routes are going to be more arduous to your average climber than they used to be, climbers who are now much stronger thanks to the proliferation of indoor walls. BTW the grading of sports routes has softened too - if you can lead HVS I can show you F6a/b routes at Buoux you might simply not dog up.
It's all going to make sport routes seem relatively easier than trad ones nowadays. So a conversion table to guide people as to how they might FEEL on trad coming from sport is probably a great idea. But that's not the same thing as how hard the moves are etc, and Rockfax, of which I'm not particularly a fan, seem to have got that aspect right.
I look forward to your table - and your guide. I bet the data in the UKC will be helpful in pitching it right too.
PS To the suggestion that trad doesn't draw heavily on different skills to sport. Pur-leese!