Well, not being a People person, I would have to guess...
but I think I picked up about 10 mph indicated - which is probably more like 5-7 mph in the real world.
But it also depends on what 'derestricted' means. I generally think of it as removing the rev limiter and putting in the derestricted drive boss - but I have heard that some people have found restrictions in the air intake. Also, for the Agility, the restricted version commonly has a #80 main jet when it rolls off the factory floor - while a factory model without the restrictions has a #82. So if you don't upjet (okay, I haven't done this) you won't see as big a difference if you take out the rev limiter and restricted drive boss.