As too panniers bringing on a weave, thought I would answer this since I have more experience than most of riding a Ducati with panniers.
The manual for the ST4S states that panniers shouldn't be used at over 120kph-really! Well I have had an indicated 146mph on mine 2 up, bolt upright (you try getting down with my tankbag) and I have to say at that speed it did weave a bit-mainly in and out of the traffic
(This was on the Italian A1 2 years ago) Last year with Jo on the back we clocked 140 once and over 130 loads of times with no weave at all-I would guess the Multistrada would be similar.
John