In general, the most profitable way to sell is by dollar amount. People that buy eighths have a much more clear idea of how much they should be paying; you can get away with higher unit prices if you advertise in $20 bags, $40 bags, etc. If someone asks you how much is in it, give them a straight answer - cheating people out on deals is not cool. However, there's nothing wrong with offering a particular deal so long as you give people what they paid for (on your price scale, of course).

If, for example, you'd normally sell an eighth at $40, you could probably sell 40 sacks with 2.8-3g.