The DH race bikes are actually gonna be lighter than a full fledged Freeride bike, such as my 50+ pound Banshee Scream. A downhill race bike will often weigh in at under 40lbs.
Although FR and DH bikes have different Geo and wheelbase, I would go with a dedicated FR bike because you are still very capable of riding downhill, where as with the DH race bike you are less capable of Freeride.
A "slopestyle bike" may be a good idea, but they do not have long travel, and even though you had only mentioned 6" in the front I assume you want a longer travel bike all around. Although I could be completely off.