Size of a scalp needed to be profitable?

[Card08]

I am a part-time bonus whore with an 11-12K bankroll, and I am looking to break into sportsbook bonuses and scalps as a side opportunity. I found a scalp for an upcoming game at +158 and -155 for the respective sides.

Assuming I can devote 5-6K to scalping ventures, what kind of differential do I need to find in my scalps to make this worth doing?

What kind of proportions would I need to bet on the line mentioned above to lock in max profit?