Hi,
The speed rating is not related to the vehicles top speed. It is a safety inbdication that if you drive at that speed for any length of time the tyre will suffer.
I am guessing that the speed rating is not below 80mph and so you will not be exceeding the speed rating and so they will be fine if you stay below the rated speed.
Please don't expect too much from any tyre, slightly taller tyres MIGHT improve the comfort slightly, but it will not transform the ride.
As someone driving around on 19" wheels on his A2 with 35 profile tyres I can tell you that it is still perfectly comfortable (firm yes, uncomfortable no).
The best way to improve the ride is to make sure that your shock absorbers are in good condition , your tyres are not over inflated and that you use good quality tyres. The stiffness of the tyre wall can vary greatly on exactly the same size tyres.
I am just trying to give you my views based on my experience (46 years of driving and 46 years of modifying cars, fitting alternative wheels and tyres thriughout that period), I hope you take it as just an honest personal opinion and trying to help.
Steve B