Of course you should always drive at what speed you (and your vehicle) feel is appropriate, but with all due respect saying "I always drive at 50 max" on a 60mph road is potentially frustrating other road users who would consider the conditions safe at 60. I find following someone at 50 slightly aggravating, however, only mildly so, the ones that really cheese me off are those doing 35/40 max on said road, particularly where I live as there are few if any places safe to overtake. I think when you get to that point it may be time to take stock and see if you are in fact still ok to drive a car/bike.
When I did my BikeSafe course with the MET Police a few years ago they were at pains to point out that exceeding the speed limit is sometimes required in order to be a safer driver, don't think that would hold up in court though, nor being on the opposite side of a country lane so you can see round corners better!
Paul I'm sorry but your last paragraph reads badly, in the case you mention you should perhaps slow down slightly and pull back in so as to not impede others?