Well, assuming complete independence would just be 1% * 1%; but there does seem to be a slight negative correlation between psychopathy & IQ. Complicating matters is Hare and Babiak's research into business psychopaths, where they estimate they are over-represented by a factor of 2-3 or so, suggesting that the negative correlation may be skewed by the 'failures' in prison samples (which are the samples for most studies, for obvious reasons); smarter psychopaths are far less likely to resort to violence**, further hindering identification (since impulsive violence is one of the major diagnostic hallmarks). To the extent that the gifted 1% avoid business, that may restore a negative correlation / underepresentation. Finally, psychopath's impulsivity and few long-range goals or efforts (another part of the diagnosis along with glibness/manipulation) suggests that to the extent genuine objective achievements cause you to be considered a gifted 1%, we can expect still more underrepresentation*.

So guesstimating further, I'd say in a population of 300m people (eg. the US), we could expect substantially fewer than 30,000 gifted psychopaths (0.01 * 0.01 * 300,000,000). Phew!

On the other hand, they would be the ones who would do the most damage and be least likely to ever be diagnosed, so we may never know for sure...

* Which makes me wonder about high IQ societies, now that I think about it. My vague impression was that they tend to collect those with poor social skills, and also with fewer objective accomplishments & success. So if you meet someone in a high IQ societies who seems very charming and empathetic but lacks objective accomplishments, just how much does this increase the psychopath possibility over the 1% base rate..?
** Covered multiple times in the Handbook; first relevant paper seems to be "Psychopathy and Aggression", Porter & Woodworth.