AN ALL-TOO brief sampling of the 6 Series teased a taste of drivetrains that are among the best on offer by BMW.

The 640i in droptop guise is – at 235kW and 450Nm – one of the heavier at 1820kg and the least powerful of the trio trotted out for a drive and it feels it, making the turbocharged six work to get underway at anything other than a genteel but brisk pace.

It's not that it feels a slow vehicle, until you drive the others …The roof is well insulated from the persistent rain and the cabin is only intruded upon by the burble of the now-standard sports exhaust.

Ride quality resulting from the adaptive damping Comfort mode is well controlled and lives up to its designation switching to Sport or Sport Plus mode certainly tightens up the handling but it also amplifies the jiggle through the chassis that comes from losing the metal roof.

There's none of that in the M6, which feels lithe, lean and muscular to the point of distraction and licence destruction.

It feels half a tonne lighter on its feet and still manages to ride with some small sympathies to the derriere, while the twin-scroll twin-turbo V8 will deliver 441kW and 700Nm when the Competition Package is fitted as standard fare.

The test car wasn't completely to that spec but given the rain-soaked slippery roads the extra kiloWatts and Newton metres were not really missed – it still led the electronic traction aids a merry dance with an unsympathetic flex of the right foot.

Despite the forced-induction system, its powerplant still manages to deliver a decent soundtrack as the horizon rushes up in the narrow windscreen, at which point you are thankful for effective brakes and steering that does as instructed.

But the final act was left to the 650i Gran Coupe and it delivered the sort of performance that might just put it on top for the best brutal all-rounder.

A twin-turbo V8 delivering 330kW and 650Nm is nothing at which to sneeze and neither is a 0-100km/h sprint time of 4.6 seconds – just half a second slower than its M equivalent.

The four-door Gran Coupe sits on the road comfortably, riding lighter than its kerb weight suggests and with aplomb in both the cruising Comfort and Sport modes, still managing a malleable ride in the harder core Sport + mode.

It's pace is considerable and the opulent, leather-trimmed cabin is unfussed by any frenetic activity under the bonnet or within the wheel-arches.

Four occupants are well catered for in space, seat comfort and cabin quietness within the Gran Coupe and its breadth of capability puts in top spot as a phenomenal all-rounder.

It dwells in a rarified pricing zone but the 6 Series offers more for the considerable asking price than ever before.