Shooting 150gr won't necessarily reduce accuracy....but it will with MOST bullets. Especially pure lead. Cecil at Precision Rifle tried to tell me that there is no reason their pure lead bullets won't shoot accurately past 2000 fps, but none of my 3 guns (or 4 guns owned by friends) have ever pushed one past 2000 fps with MOA groups.
I shot my Traditions Lightning with the 195gr duplex DC (Redhawk's favorite) and it was great up to 100gr, where I hunted it. My Omega wouldn't shoot it under 4-inch groups at ANY charge, so now I shoot Shockwaves. I hunt with the 200gr Shockwave at 110gr 777 (2100 fps), and can shoot the 250gr version up to 120 gr accurately.
I have never found any bullet that will maintain sub-1.5" groups at 150gr in my guns...but I know people who have. Personally, I think the only need for 150gr on deer is if you're going to be shooting long range, and if that is the case you need maximum accuracy anyways so I stick with 110gr.