Sightmark makes decent stuff and their Pinnacle line is high quality, the CORE series are a budget, Chinese made optic.
Your choice is not really a good one. i have no experience with their CORE series, but when you start talking about very high magnification scopes, glass and coatings quality becomes critical. Also, the 1/8 MOA adjustments are very fine, unless you are shooting F Class, they are too fine.
I would suggest something in the 3-15 or 4-16 range in that price bracket.
Depending on your location and availability, you may want to consider something like the Falcon Menace 4.5-18. It is a much more usable magnification range and it also offers several benefits over the CORE. The falcon is also a Chinese optic.
I like Sightmark and have dealt with them on several optics, with two of them being Chinese manufacture. The quality seems very good and the glass does seem decent.
