> So far, I've mainly been using consumer grade Kodak Gold 200 (or 400) film
> and I'm wondering if I'd get more consistent color and exposure between
> images with higher grade, slower film. I plan on shooting some Fuji Velvia
> and Provia slides soon, so I guess I'll find out if that makes a
> difference.

Velvia is not a good idea as it cuts down on your dynamic range.  See the 
bottom of 
http://www.bigbenpublishing.com.au/360/docs/tutorial/advanced/dig_film.html 
for a comparison of slide and negative.  I shoot Fuji Reala which is good 
in mixed lighting and provides a good dynamic range.  I should test other 
colour neg films but I haven't yet.
Cheers

Ben