If you practice enough to hit what you aim at and are cool under pressure so that your shots will still find the mark, then 9x18 is more than enough. If shot placement is poor, then a 10 gauge slug is not enough.
I like the PA-63 but found them less dependable than the Makarov. I consider accuracy and dependability the senior factors.. Many people consider the Makarov the most dependable pistol ever made... and one of the most accurate.