If you're aiming for the Ttar duo (the most common use for 6 maxed machamp squad), the 6 Machamp setup usually gets through fine, but things may get ropey with Iron Tail+ Fire blast moveset. For this purpose I advocate 5 Machamp+1 Hariyama, it should provide more than enough cushion for you to finish the raid in time and not faint out, for all movesets.
For Aggron duo, Hariyama is not good enough.
For Absol duo, you can do it without maxed machamps anyway