I have not shot the VS, but Ektachrome 100G and 100GX were favorites of mine that looked just fine at 100 using an incident meter. What you could do is shoot each frame twice, one at normal EI-100 exposure and one a half-stop under. With the G and GX versions, a third stop didn't make a great deal of difference, a half stop less exposure came out a bit darker than normal. The VS might be different. I'd just use one roll and shoot several scenes at normal, 1/2 under and maybe even one stop under. Develop it and see what versions you preferred, then shoot everything else that way. You'll waste less film experimenting if you use one roll to test and shoot the other four the way the tests indicated was best.