Actually been playing around with the FAS a bit more and came up with this:
http://coriolis.io/outfit/federal_assault_ship/06A6A5A5D6A4D4C1e1e272704040404p25i35---.AwRhrSqiSA==.Aw18cQ==
406 m/s (as fast as an FdL)
490.8 MJ shielding (same ballpark as Vulture and Clipper shields)
5 A shield Cell
Turns and maneuvers like a Vulture
16.97 LY jump Range
Mass locks Factor of 14 (Clipper and FdL have 12, Python has 17)
2 Large, 2 medium hardpoints with excellent convergence
4 utility internals left over - can keep spare offline shield cells here.
So, IF you can get prismatic shields on it, I'd say it's a straight upgrade over the Vulture, and pretty nice relative to the FdL. With it's speed and maneuverability, the 490 MJ of shielding is plenty - and in the long run, all those internals mean you have more overall shields than an FdL due to cells.
Does it replace the clipper? No. The clipper is still much faster and has better internals.
Does it replace the FdL? Maybe. It has much better maneverabillity, much better jump range, better mass lock, more efficient hardpoints, more and better internals (meaning more shield cells), fewer power management issues (it easily fits prismatic shields with power to spare).
If you're willing to make the trade of raw shield capacity for shield cells, than the FAS wins in every way IMO.