I guess I'm a little late but anyways, I shot a two day assignment recently with fuji superia 800 (which apparently is a relabeled Fuji Press 800).
It has very pleasing acurate colors and the grain is suprisingly fine for the speed, I was impressed.
I exposed the opening gala/dinner whatever at EI800 as the lighting there was scarce (and yellow! ugh...) and next days events/lectures etc. at 640.
The lighting at the dinner was a nightmare, they had neon and yellowish tinted regular bulbs with very high wattage (sp?) and I was worried the negs would have a terrible yellowcast but to my suprise they turned out great colorwise, the film is very forgiving to mixed lighting.
The lighting at the convention wasn't as bad as the first day but still they had those yellow bulbs burning so especially the bald people looked kind of "yellow" during the shooting, which translated to a slight magenta/yellow cast on their heads on the film. easily correctable though, and certainly not the films fault.
So to say, it held up very well colorwise though I haven't tried any other brands 800 C41.
The grain is as I said quite fine, BUT very dependant on the right exposure.
It was kind of weird to see slightly underexposed shots look so different.
I'd recommend shooting it at 640 to avoid underexposure, but 800 gave great results too so it really depends on the situation I guess.
The examples are not yet worked over and there is considerable shadow detail in the dinner shot despite the 800 EI which you probably won't see at this res.
Sorry for the bad shots

(at least they repay my daily roll of acros 100)
Hope you had fun shooting!
Phil