GR4s are taken to 1.25M on post maintenance flight tests (I cannot remember what the F3 is taken to). The 2250l tanks are cleared supersonic on the F3 but not the GR4, although structurally there is no reason why the clearance could not have been obtained for the GR1/4; it just was not needed.
There is a somewhat excessive use of the adjective "easily" on this thread when applied to the speeds which the Tornado can achieve. Yes, an F3 can reach 800 KCAS and 2.0M, but with stub pylons and missiles I would add a slightly more conservative tone!
The last remaining GR1, ZA326, achieve 709 KCAS/1.06M at low level on its penultimate sortie (7 pylons), but this required a shallow dive. Unfortunately, a R THROT caption precluded squeezing any more out of it!