I am still in the testing phase.
BIN, generally, has proved to provide stable sales revenue most months. My best ccTLD month was in fact last month when I had most domains on "make offer". I was able to negotiate a £3000 sale for a .CO.UK name (HotelPay.co.uk), something I could not have done had I had the name with a standard £500 BIN button. But, if that "outlier" sale has not occurred, the month, in terms of ccTLD sales, would have ended a little lower than a few BIN months - but the difference would have been fairly small (-10%).
For mid-range to higher quality domains, "make offer" gives you more upside/opportunity to close better deals, maximizing revenue. I think the key could be to keep a % of the portfolio synchronized with BINs, and leaving at least 35%-50% on "make offer" - so you are going to have the opportunity to closer higher deals/generate more revenue at least 1/2 the time. Testing still in progress, however.
More important than anything is picking the right types of names.