It will help, and also helps immensely with getting a sight picture when shooting on the move or on a moving target...but fundamentals still apply, and a lot of that is going to fall apart under fire. I'd definitely rather have it than not in that situation, though.I'd say 20yds and out an RDS is going to speed up you being on target, and your accuracy will be improved immensely.
Personally I think in this situation ( a crazy with a rifle trying to kill ) an RDS would be a must.