"If SBD is trading below $1, you would be better off (at least initially) electing to receive you post in 100% SP instead of 50/50. "

That depends what you are looking for. If you want to get as much SP as possible on the day the reward is issues, yes, Power Up 100%. However, if SBD is below $1 the witnesses will begin to issue interest payments for people who hodl SBD. Personally, I like the idea of getting interest on my SBD while I wait for the price to go up.