Delta is running quite the sale in between Boston and Denver. A ton of dates, including weekends this winter from Boston to Denver and vice versa. If you route through Atlanta, it comes to 4,290 elite miles for $130, or 3 cents per elite qualifying miles, which is pretty awesome. Plus, you can even go skiing at some of the US’ best mountains (of course adding onto the price of your “mileage run”).
While its early in the year to be thinking of mileage runs and hitting elite status, since Delta has MQM rollover, theres not much risk in accruing more MQMs than you need since you should be able to roll them over.
PS these fares work as one ways as well.