Not sure about Voiceover work, but these are very clean mic pres. We own some 7602's as well which are more "neve-esq" but the 581's seem to have clean highs and a slightly boosted mid range.
I'm actually looking to sell ours because they are a bit "bright" and they are basically brand new. Going to invest in some more Neve gear. If anyone intersted message me. I have 2.