Seems like you have quite the decision to make.
For 100 laps, what ever prepping you do should probably be on the inside. Never raced on EL's, but from what I have read it seems they are typically worked from the outside in the dirt community correct? I can assure you what ever typical mild bite you would use like Hot Lap 2 will come right out of the tire by half way totally changing the way the kart handles. If it were me, Id probably only wipe Acrysol to help the tire fire on the start and thats it. This way, you can tune with mechanical grip and air pressure. You will be able to make the kart more consistent for the whole run. If you rely on the prep to make speed, your kart will probably fall off a cliff after 50 laps.
I do like the idea of Vega Whites, maybe even go for the Blues which are a couple points harder than the whites but still softer than the EL's. I think that will give you more grip than the EL's and they won't fall off as bad as a Yellow, a Maxxis or Firestone might. Like it was said before, you might lack ultimate qualifying pace but you won't fall off after 30 laps. You will have a kart for the long haul.