The best scope for the money is a used AN/PVS-5 with at least GEN II Image Intensifiers in them. The PVS-5 has a very large focal objective which collects more ambient light than smaller objectives. This permits you the highest resolution of target available. The scopes that mount to your day scope are problematic. First, the issue of alignment of two separate optics is a real ball breaker. Second, as stated the smaller focal objective collects less light, thus presents less resolution. Third, the image on the back side of the image intensifier tube is magnified by the day scope (8x, 10x) thus presenting a very grainy picture to the shooter. It would be cheaper to designate one rifle as a night shooter and dedicate the night scope to the rifle than to attempt to have one rifle do it all. BTW, rifles are a lot cheaper than quality night scopes. Just sayin. With your range requirements you could easily get by with a rifle offering 3 minutes of angle inaccuracy.
All great comments. The thing about being a freeper is there is an expert on almost any issue. I can dedicate a rifle, but I have an Aimpoint on one .223. I am going to look seriously at the PVS-5. I have to get this purchase made before hunt in September. Thanks again.