1x12 speaker to approximate G12M Greenbacks in a 4x12 cab

[jaymenon]

The Celestion 'Greenback' G12M25 is recognised as the ultimate classic rock speaker. But that speaker is of course traditionally used in a 4x12 closed back cab. So really one is describing the sound of a 4x12 cab with Greenbacks...

From personal experience with PA speakers - a single 6" speaker sounds very 'mid-rangey'. However, a cab with a vertical row of four such 6" PA speakers will give you a lot more treble and bass (i.e. it 'expands' the frequency spectrum at both lower and upper ends)

My question is - in a 1X12 cab, which speaker best approximates the sound of a 4x12 cab with Greenbacks?

I'm not talking sheer volume, but tonal similarities. Intuitively I'm thinking it must be a speaker that has a wider tonal spectrum - more lows and highs - than the Greenback...?

Expert opinions most appreciated.