main_dog,
Regret I cannot assist in that area. (And listen, we're talking about roll RATES, not rolling!)
Unlike its big sister, the VC10, the One-Elevens all employ manual spring-servo-tab ailerons - not PCUs. Spoiler/Speedbrake surfaces are hydraulically powered, of course.
According to my hand-written course notes (in Doug Realff's lectures at the Bee Hive in 1977, re the 200 series): when speedbrakes (why don't we call them AIRbrakes?) are retracted, they do not lift as roll spoilers until 4deg of aileron, unlike the cruder system on the B707. This avoids spoilers cracking open in gentle turns or with aileron trim, and reduces initial roll rate. 4deg of aileron represents roughly 11 - 15deg of control-wheel movement.
However, with 10deg of speedbrake (half the maximum permitted in flight), the situation is slightly more volatile.
"...as soon as the (control wheel) is (fully) displaced, the spoilers will rise on the downgoing wing (to 43deg)......and the spoilers on the upgoing wing will retract. In this config, maximum roll rate is about 400deg per second."
Returning to the speed issue, the spoiler surfaces are designed to "blow back" at a certain air load. This would probably limit roll rate at high IAS, and presumably applies to all aircraft types. FBW types, no doubt, prevent that happening by limiting roll-rate (although blow-back of the surfaces can still occur in speedbrake mode).
Chris