Is this load too slow to be trusted for woods-protection in the lower 48 states? Should I bump it up to the full 24 grains?
That load will whistle through anything you are going to find in the L48. The only issue you may have is lack of stability. But if it shoots well and you aren't keyholing then I wouldn't worry about it.
If you want velocity, you can drop your bullet weight back to a 335 or 325 gr boolit. Down in the states I would even feel comfortable to a 300gr or less.