The usefulness of Velvia in Iceland depends on finding a scene, or scenes, with strong colour in them and wrangling Velvia to either modulate them (as close to natural) or boost them -- either with or without a polariser (in diffuse/overcast conditions only, which is what Iceland is renowned for!). I would be inclined to hedge Velvia up and down from box speed to suit conditions, that is to say, sometimes I rate it at EI64, at other times, EI40. A lot of people think Iceland endears itself very well to B&W photography, because the landscape -- variously described as bleak, lonely and coarse, can be very monochromatic, almost bland in its presentation, and using Velvia (or any colour film) on a scene with scarcely any colour in it won't necessarily 'lift' it. Tim Rudman's book Iceland: An Uneasy Calm has thrilling atmospheric B&W imaging in it when demonstrates the pervasive drama and majesty of such a rough landscape.