Ok, I assumed you were using manual targeting. I personally try to set up 90 degree shots 90% of the time for which the pull out tables for the different speed torpedoes comes in handy, it also negates the need for distance to target and AOB (as you already know this will be 90 degrees). As for target speed, you'd probably do well to use the 3.15 minute rule to work this out by plotting the ships position on the map. If you have Map Contacts on you can easily work out AOB using the map too.
Believe it or not, by using manual targeting you may make your life easier, in that you can do most of your calculations from the peri view without having to switch back and forth to the map. Give it a try.
