Bell gigabit plan here too. With direct connection using the bell sfp to the USG-PRO, could only manage 600 down, 600 up. With the HH3000 in bridge mode and using a cat6 0.5m cable, down is 950 up is 750.
This is the same behavior I've experienced, I'm using a TP-Link MC220L because I couldn't get direct SFP working and my speeds are down substantially on my UDM Pro.
I can't seem to find a good guide that's helped me get SFP directly into the UDMP to try that out... But considering I'm using all of the threat management stuff I suppose it's not the end of the world.