There were several recent discussions here about max range on red dots and such that have some info you might find interesting, but here are my $0.02

Red dot range- If your eyes are good,the target contrast is good, and you have a good quality red dot with a small dot size and no smearing/bloom then 150 yards should be easy. If any one of those criteria are not met, then IMHO it would not be something I would use. In my experience, picking out a deer from the wooded background at dusk through an unmagnified red dot is not easy or guaranteed or even possible for me with my eyes.

Scopes- like anything, you get what you pay for. I run the variable mag leupold on most of my contenders. I found the low light performance (contrast and clarity) of the leupold to be the best IMHO and would expect the fixed mag scopes to be better. For 150 yards a 2x (discontinued i believe) or a 4x would work fine and help keep the cost down. I like the flexibility of the variable.