Hey, Graham,
Here are the 12" speakers I tried and the results
Single speaker in 40 Watt DSL40C:
Celestion G1275H - blew cone off voice coil bellows
Twin Speakers in 2x12 Cabinet powered by 40 Watt DSL40C:
Pair of Celestion G12M 25 Watt -
blew cones off both voice coils
Response from Celestion Post-Inspection - "Speakers received excessive power."
(LOL Typical response trying to justify

quality.)
WGS 50 Watt 55Hz Reaper in DSL40C
Subdued highs
Zero issues
Jensen Jet 100 Watt Stealth Neodymium
Great speaker with subdued low end
Zero Issues
Jensen 80 Watt Stealth Neodymium
Very well rounded speaker
Zero Issues
Electro-Harmonix 12VR75
Zero Issues - very pronounced midcrange
I did play through a pair of borrowed Celestion Goldbacks at one point, but I didn't dare push them.