Provia 400X and Velvia 100 are my favorite slide films, together with Astia which is now discontinued. Yes, Provia 400X is more grainy than the others but it is still a very fine grained 400 ISO slide film (the finest of all!). Its color reproduction is very accurate still the slides have a punchy and crispy look to them. Contrast is not overly problematic. This film is very suitable for pushing. I pushed it to ISO 800 with very good results, though it became a bit more contrasty then. I have also seen pictures made with ISO 1250 or 1600 and they were fine, though somewhat dull and grainy. At ISO 800 it was hardly discernible from ISO 400.
Velvia 100 is my main film for landscapes. Great punchy colors and sharpness, very fine grain. Colors look accurate to me, but they are enhanced. From what I´ve read this film does not alter skin tones as extremely as Velvia 50, which often gave a sunburnt look, but I have never shot Velvia 50 myself.