Andy, I gave up trying to bend 50mm stainless, it's fekkin tuff stuff. I can happily bend 25mm x 1.6mm wall in a standard pipe bender if I pull gently on the tube as well as on the handle. My formers only go to 180° though. I solved the 50mm bending by buying pre-made bends and welding them to the tube. You can get bends with a really tight radius.
I saw some crackin stainless bending work outside of a new Argos store locally....I have to admit I had some bad thoughts about an angle grinder and 2am....
I've used a company for mail ordering bends because part of the problem is knowing what is available so you can get your local stainless stockist to order for you. However, I'm fekked if I can remember their name. I'll look into it for you because their web site has a downloadable PDF which contains the sizing info which you might find useful.
Here ya go. Nexusflow
and PDF for bends.
I'm not recommending them because they made a mistake in what they supplied but it came right in the end.