Ive recently had the same problem, going from 6.2/ 5.8 m ribs to a 7.5ribcraft.
To be honest the difference is pretty negliable. We tow 130 miles each way regularly, even narrow country lanes. The key being to plan ahead more on the journey and try not to get youself into precarious situations. As said before pick your fuel stations in advance if possible making the exit as easy as possible.Slip ways can allso cause minor problems especially with weed on them, my last trip saw the jeep sliding back down the slip slowly, so i allways carry wheel chocks to deploy when needed. I do think that 7.5m is the max for me, as all our boating is trailered. and supposed to be fun.