roe hunter, darlin', we gotta quit meetin' llike this...
While I don't think it matters for the Speer, jacket hardness will make a pressure difference. The Winchester Fail Safe bullet, for instance, gave me signs of pressure--primer flattening--when I used my standard pet load with 4064. In a casual hacksaw blade test, the FS bullet jacket is harder than the Sierra.
I've been using 52.5 grains of 4064 with 150-grain Sierra, Hornady and Rem Bronze Points since 1950. They all perform about the same on deer and in groups on paper--and through at least three different rifles.
Seat of the pants, I think maybe 4350 is a bit slow for the 150-grain. Better with heavier bullets, but don't ask me why--since it's a recommended powder for the .243.
I've loaded some 180s with H414, but haven't tested for group size, yet.
More FWIW ramblings: I've long used 3031 in the .243, for the lighter bullets: 40.0 with the 70-grain Hornady Spire Point and 37.5 with the Sierra 85-grain HPBT. Very tight groups. My Sako's twist rate is apparently a bit slow for the Nosler 100-grain, so I quit bothering with the heavier bullets.
And now, back to the scheduled program...
, Art