A saddle is only as good as its position on the bike. Good positioning will not cure a non-fitting saddle, but the best saddle can easily become uncomfortable by less than optimal positioning.
Saddle fore-aft positioning is one of the most important (if not the most important!) determinants of comfort and performance on the bike. Yet many seat-posts have long clamp bases while saddles have short rails. This will leave you with a very small range of adjustment.
If you are in the market for a new saddle, you will want to try it before purchase. But do not forget to check the rail length. The same goes for the seat-post. Though you are unlikely to be testing we still recommend you to choose one with a practical clamp mechanism and favour one that has a short base.