One of my last years upgrades was a carbon fibre propshaft from CTG. Not sure about it´s strength before I can now confirm that I couldn´t manage to break it yet... Some racing, some track days, a few 0-60s, no sign of a ripped propshaft. My Cat has 280BHP (VX of course... 😬), 6 speed sequential box, running on Michelin slicks.
Now that I couldn´t rip it apart yet it´s all down to it´s long term strenght probably. Hope it´s gonna last a few years now but until further experiences I can only vote for the CTG propshaft.