I just got a Bushie flat-top upper with the Superlight barrel  I will order an Aimpoint soon, but am undecided on the mount and BUIS.  

I like the LaRue (for both) but don't know how they work with the non "F" front sight base/post on the Bushmaster.  Does the taller (screw-in) front sight post work OK with the M4 milspec BUISs?.  Can the "F" base be installed by someone (I may get a foreend that requires FSB removal anyway.  Does anyone have this set-up that could comment on it?

The only way to know for sure is to shoot it. I haven't needed the taller front sight post on any carbines built with Bushmaster barrels.

That said, I do have a .04" taller post in the range bag as cheap insurance. I have needed it both times I built 20" flat tops using "non-F" barrels from both Colt and Bushmaster.

The LaRue BUIS is the cat's ass. Haven't felt a need to switch from the ARMS/Aimpoint combo yet.

My first thought was to get an "F" FSB from BravoCompany and avoid the whole front post adjustment bit.  It looks like my Bushy superlight barrel id only 0.625" diam. though and wouldn't accept the M4 milspec FSB.  So, I think I'll follow your advice and just give it a try as is and get the tall post just in case.