I have a Mac Pro with a FW800 port. I can daisy chain a LaCie 800 drive that has a FW400 port with another LaCie FW400 drive. Both work - I've never bothered to measure the speed.

iMac (19,1, 3.1 GHz i5, 12.7.4, 40 Gb RAM); MacBook Air (1.8 Ghz, 8 Gb RAM, 10.14.6, 256 Gb SSD) Vodafone router and Devolo Wi-Fi Extender, Canon TS8351 printer/scanner.