Harry's right about your low RPM limit taking speed out of the equation as a variable, but rocker deflection is related to spring load. A cam with high accel rate (in .001" per degree of rotation) needs more spring for the same RPM.
A good replacement is fine with 250 lbs., but for 400 I'd use steel with a roller tip but a plain shaft. Ask the cam manufacturer about this, not the phone guy at Summit.
You might wind up with the same stuff anyway, but I always feel better knowing that nothing got past me, and helps diagnosis tuning stuff afterward.
