I am a 275er, but I am temporarily one of those 300+ guys. I can tell you what not to take... anadrol. I swear, everyone I know who takes that stuff gains as much fat and water as they do muscle.
When I am back at 275, test is great because of the it is known for creating lean body mass and cutting fat. Some of my buddies who have been juicing for a while, who are also 275ers, use test, deca and anavar with either winstrol at the end of a cycle or a clen/T3 combo.
Prolly most important for being a 275er, you need to keep your calories, carbs, fat and protein accuratley. Big guys, in my experience tend to have a slightly slower metabolism than some of the smaller guys.