Is that sorta trial and error? At the moment, my 2.6 with EFI does fine with the stock 9" clutch (LUK kit so I think it's a Sachs disc) but if I did a 3.0 or 3.2 M104 I wonder if it wouldn't be enough. As you've pointed out, I probably don't want to do business with the manufacturer that made your clutch, but what other options are there?
I am somewhat considering using a BMW 6-speed manual for whatever I throw in this car next though, so I would have more options then.