It is the 2x1.8 rear pistons that cause that feeling.
Ran a full day (nearly 8 hours) at Kidderminster with mine.
B6.1D ... so much forward drive it's silly, on a par if not slightly better than my B6D stand up, corner speed nearly as quick as the laydown in the same car.
Drying track stopped play.
B6.1 .. even on the kit setup it was obvious immediately that the car was more than the sum of the parts.
Has a lot more steering than the B6 and generates far more forward drive too.
By the end of the day I had a really sweet handling car that was easy to drive and quick (had an F1 driver there for some of the day so had a pace setter).
Changes from the kit B6.1 setup (other than building it with hard arms and alloy front bulkhead)
Front bar from blue to white
Front oil to 37.5wt
Wheelbase to medium on rear arms
Removed rear ARB
Rear shocks changed to 27.5wt/2x1.7/grey V2 spring
Added 35g under the LCG lipo I was using, total weight of car 1555g.
Tried lots of other stuff but kept going back to the kit setup for reference and like the longer links.
If the grip wasn't quite so high I'd be tempted to go back to the more customary set middle hole in front bulkhead and middle hole on the rear camber plate.
I strongly recommend starting with the kit setup and tuning from there, if you bolt on your old B6 setup you might miss some of the benefits of the new car
As for the B6.1D I didn't get chance to change much as it dried really quickly.
At Coventry this weekend Dave Searl ran his B6.1D to great effect, kit setup other than shocks on the back & softening oil 1 step in the pouring ran.