Wayne(OP):
what format are you intending on using? 400x is available in 35mm or 120, so you can use it in a MF camera no problem. RVP50 is available in 35mm-8x10, so if you're planning on using a tripod, you have many options.
here's how I've found Fuji's slide films to work for me:
Velvia 50(35mm-8x10): great film, too saturated(IMO) for shooting people, can accentuate certain colors(blues and GREENS) more than others.
Velvia 100(35mm-8x10): "..." a tad less saturated than the 50, but a stop faster. I generally have rated it @80 to keep shadows from blocking up completely
Velvia 100
F(35mm-8x10): less saturated, less contrasty than 50 or 100 versions, better for a boost in saturation, but not "over the top". Works nicely with skintones IMO as well.
Astia 100F: personally, my favorite of Fuji's pro emulsions. 35mm-8x10 sizes available, has a warmer tone standard. Works perfect(IMO) for just about everything, less contrast, great for skintones.
Provia 100F(35mm-8x10): my 2nd choice personally(35mm-8x10), super sharp, super fine-grained, beautiful film. Shadows go blue quickly, but a slight warming filter(81c) helps to tame that for open shade shooting.
Sensia 200(35mm only): nice film, a little warmer than Astia. This is only in 35mm that I know of, getting harder to find than the pro emulsions. Nice film, similar(IMO) in warmth to Kodachrome 64(especially in late-day shooting).
Provia 400x(35mm, 120): The only 400 speed emulsion left in chrome. There's E200 from Kodak(35mm only now though), and that can be pushe to 800 perfectly fine(E200). 400x is great b/c its available in 120 as well. Not super fine grained, but its the only game in town. I like to rate it @ 320 for a tad overexposure. Handles skintones nicely, even in failing light. I've pushed it to 800 before and it worked great!.
there's also Kodak's offerings, and they're actually my 1st go-to's when I can get them while in stock at my local stores.
E100g(35mm-8x10): Probably the best slide film IMO I've ever shot, not as good as Fuji for reciprocity(up to 10s no change in time or filter factor). Comes in 120(my primary format), if you use filters(LEE, Cokin), this film can pretty much do anything you want color-wise. Not TOTALLY neutral, but NATURAL color balance. Works great IMO even if pushed 2 stops to 400(more grain, contrast however of course). I rate it @ iso 80.
E100vs(35mm-4x5): Super great film, similar to Velvia 50 in terms of amount of saturation, but more NATURAL saturation, not just "lets slide it WAY more" like Velvia(again, IMO). Nice film, works ok for skintones too.
Elitechrome 100/200(35mm only): nice films, haven't shot too much of either, but they work well. Cheap compared to pro emulsions, some drug stores carry it

!. Pushes 1/2-1 stop MAX!!! Any more and I've gotten crossover of color. This is my experience however. Others maybe not.
-Dan