Ok, I think my FTP is calculated correctly now. Did a 90-90-90 workout today:
90% of 20 min power (approx FTP) for 20 min, 5 min rest
90% of 5 min power for 5 (x2) --couldn't see exactly how far over FTP this was set but it was rough. 3 or 3 min rest, I forget.
90% of 30 sec power (approx 200% FTP) for 30 (x 4). 2 min rest.
Ouch.