Yep, been through this a few times but an 890 measures 89mm from centre of spindle to centre of brake block in the furthest posititon. So a 1020 is 102mm, an MX1000 is 100mm and it also applies as you get smaller so a 610 is only 61mm (used for minis with 1-3/8" rims).
I've also had a few 1080's which I imagine would really help out out you Ripper builders..... Thinking about it, it was Ash who had them off me...... ;-)