Okay - a little more dribble about the Kleemann S8 SLK55 - been doing some research. Thought I'd log it.
I persist because these power plants are similar to ours but with 2 extra cylinders.

These kits are applied to NA AMG SLK55 5.5L M113 engines. Boosting stock performance from a stock 355hp (375ft.lb) to 530-606hp (790ft.lb).

Now - I give a range here because the guy in the OP listing is reporting 606bhp (455kW), but I've read Kleemann actually detuned their package to
1) meet some international smog regs and
2) reportedly "by some" (unconfirmed) the 450kW exceeds the 7G transmission's design power capability of 750Nm (550ft.lb) not sure on this one though - someone may have some better fact sources.

Side note: 355hp is the same as our 14.5psi SRT6/SLK32 engines in stock format.

Now somehow - they only use 0.45bar (6.6psi), although I have also read some 0.5bar E85 reports nudging a little more hp.

The Kleemann S8 offering....
--6,6psi Supercharger /w Johnson CM30 water pump and sizeable Heat exchanger (about twice ours)
--cams (and in some reported cases - Ti springs and valves)
--tune + EMS*
--suspension
--brakes
--tranny strengthen (? sometimes)
--headers
--exhaust
--small intake tweak
--18" rims
--spoiler etc...
*the EMS piggy backs on the ECU to drop rpm a few microseconds prior to shift change.

7psi would take a 355hp motor towards 355 x (14.7+7)/14.7 = 524...so they must extract the additional 82hp from the other items (as well as 585ft.lb = 790Nm)

I haven't driven the vehicle - but given some here have reported traction issues with 3190lbs at 450hp...how the hell is this 3410lb nose heavy beast going to keep rubber on the road?

As for any upside potential in the boost - I think the engine might already be being tested to its limits.
I understand the SLK55's didn't come with forged pistons or any of the internal AMG niceties ours did.