I only ever shot cast bullets in straightwall myself, and my buddies who shot 7mm used 150 gr spire points because the Rams were tricky. Seems like if you're goal is to do well in competition, go ahead and move to 7mm (7-30, 7TCU, etc.) in a single shot. Personally, I stuck with 44 magnum as 1) the man who got me into shooting silhouette was Major Golden, The Iron Man, double distinguished and only shot single action revolvers "on his hind legs as God intended" for the challenge, and 2) I wanted to get better with a pistol I'd most likely use for hunting. I used a cast Keith type 240gr SWC with gas checks, over 294 in winchester cases, and saw a few Rams fall.
In general, stick with the flattest shooting non-expanding bullet that retains the most energy at distance.