I believe you can use both STEEM or SBD.

Doing it right after you post might give you that little boost, but have you seen how the payouts have been decreasing over time? 7 days is a long time to let that vote decrease to amounts that aren't really profitable anymore.

Also, manual curators who really believes in good content will overlook your post if you already have a @randowhale vote on it. So you are losing the chance to be upvoted by them. Especially by @curie. in the long run would you rather get $ or a potential $40 and upwards? This is only if your post is really good though.