The Ramshot Rifle powders all seem to preform best at full pressure, and your 45K PSI is not within that range. Doesn't mean it won't work but you will have to see by trying.
The persons giving you advice about slower powders for long range accuracy are either misinformed or you misunderstood. Accuracy means consistency and you can certainly find consistency with with medium burning rate powders like 4064.
Slower powders will help you find velocity in your long barrel but not under the 45K PSI range.
