Do you know where you can see what variant the engine is? I have a 2012 Sport GTS (registered mid Oct 2012 but in South Africa so not sure what production date) so it should be either YM or (hopefully) YT - both with reed valves but the latter has an extra 10BHP - not sure where they got it from though.
The reed valves aren't the power increase, I know Maserati made big point about them as it's a cool way of simulating the pump efficiency of dry-sump (but they didn't have the budget to revert Stradale back to dry-sump)
Where the increase came from is the cam-timing was modified and the airbox improved airflow (which a GranTurismo sport also has) they just tuned the engine further (electronically)
Now officially 2010 got the modified cam variators (INA spring type) but they weren't always installed in sequence so you can have a first batch full facellift QP 4.7 with the old variators (trust me i've had full facelift apart with old variators)
The improved variator added 10 degrees more adjustment range to the engine versus the old ones, hence the incompatibility electronically of the ECU's, late engines can move there cams much further.
YK also got DLC coated rods and i recall different piston skirt coating.
FYI F139YK in it's first 2011 irritation had 450 HP and 510 NM
With the big facilitate they bumped it to 460, and the last cars had 470, those engines aren't different.
All F136 above 440hp have the big airbox and integrated MAF sensor (i'm talking Maserati F136, Ferrari is a different topic)
So basically the VE rating of the design is capped at roughly 100hp/L, to go above this in my opinion the exhaust manifolds are the issue, and i believe the torque curve is limited due to the runner lengths and dents they have from factory.
It is worth noteing that California uses a F136YK as basis although roughly roughly speaking using 458 DI head and quad variators (cross-plane crankshaft like the maserati's!)