Interesting about the speed brakes...I'm not sure how I feel about that.
Depending on the nature of the flutter, I'd probably use body or tail mounted SB and be a bit more reluctant with spoilers.
In any case...if you do inadvertently overspeed the aircraft rest assured that the test folks will have anticipated the use of speedbrakes in this situation - throttle back, be smooth, and use 'em if you need 'em (unless, of course, the operators manual says otherwise!)