I've heard countless Radikal equipped decks and have used one for the last 5 years or so. During that time I've come across one that did have a problem, and have heard by hearsay of one other that had a speed problem. Linn equipment is normally extremely well engineered and reliable. From what I can gather these are very isolated cases and it is unusual, and certainly in the realms of less than 1% probably a lot less.
The Radikal is not so much about overall pitch stability but a change in the character of the way the way drive is transmitted to the platter. I doubt it would measure much differently to an AC motor equipped deck in terms of pitch stability but the smoother drive of the platter via the belt results in a quieter and more resolving performance. It seems to be tres fashionable to just get hung up on the price but the fact is, it's a significant improvement if you can afford it. My advice would be to have a chat with a good dealer like Cymbiosis in Leicester where you can hear the difference and decide whether it's worthwhile or not. One person's 'significant' is another's 'marginal'. Obviously bring a couple of classical piano albums to assess.