My bad if this has already been asked/discussed. Anyone used the hard 94a bottom and the stock 91a top together? No complaints with the hards, just trying to see if I can get that surfy turn a little quicker while still being stable for flip tricks and whatnot.
The dual duro bushing theroy is (this was straight from ACE ages ago/is longboarder logic):
A soft bottom bushing provides the turn. The softer it is, the deeper your turn. This is what makes your truck feel loose.
A hard top bushing provides the snap back to center, this is where your truck becomes responsive, i.e., being able to rebound back/out of the deep turn you just did.
Using a harder bottom restricts your turn (like cranking a soft one down).
Using a softer top lessens/slows your return to center
Putting a soft top (86a) with the stock ace bottom is so mushy and out of control it's crazy unless you weight 50lbs

and likewise, doing something like a 100a top and a 96/94a bottom just ends up being tight and you don't get that dual duro combo like with ace.
This is where the 90a average comes into play.
94a bottom and 91a top are close enough that I doubt you'd really notice that much of a difference than riding the same duro in each spot...ACE 'mediums' are only 5 duro apart (86a bottom 91a top) but I believe that's the 'magic' combo for that geo (probably after ages of trial and error of different duro combos).
Mixing and matching is the best way to find what you like tho. I've dabbled far too much with bushings and from what I've found, ACE and Royal are the only ones that really work/benefit from the dual duro bushings, probably because they are both so squirrly out of the box to begin with. Indy sort of gain a benefit but (for me) only when using conical bushings (at the cost of that smooth stable long drawn out carve) it makes them more snappy (88a conical bottom/92a top), espcially with Bones med bottom/hard top.
You could always go krux 92 bottom / 96 top if you wanted to keep that dual duro vibe. Problem is finding taller harder bushings that fit ACE.