Next:1M added to my machine
Not too easy, because this machine has a lot of hacks : 6Mhz SMD Turbo Card, 7.12 Mhz turbo, switchable color/mono composite video, internal speaker mute switch, external keyboard connector for rewired PC keyboard (20 years ago there was no new membrane currently installed brand new from RWAP ) Miles of wires
And now adding 10Mhz turbo

If a game would load all of the one megabyte,

for what time would it load ?

You must tell us how to modify the Enterprise for 10Mhz, as I feel I might have to do this for my Arabic Enterprise once I'm happy it's all working properly (replacing all the caps at the moment!).

Ok I will start overclocking topic

3840 seconds at 2400 baud, calculated with approx 1.5 second breaks between two 4Kb blocks
It would take only 64 minutes, only some coffee breaks

Now I'm running the Small Demo for least two hours at my 10MHz machine, with the 1MB expansion. And it is looks stable previously only tested with little BASIC programs.

The digi sound samples are very funny when played at 10MHz Dave generated musics still music because the player program synchronized with the 50Hz video IRQ, just playing in higher octave

How can the 10MHz Z80 clock influent the dave frequencies ? Is there a hardware incompatibility betwen the DAVE and 10MHz solution ?

Dave always running on System Clock (2xZ80 speed), if you raise the system speed then Dave also running faster, sound frequencies will be higher.
For the 6MHz machine (12MHz System Clock) can be adjusted the Dave on the port 191 (BFh), then it is can generate same sound frequencies as the original 4MHz (8MHz System Clock) machines.

But in the future programs this is can be handled by software, just need recalculate which sound frequencies sent to Dave.

but the sound will be almost broken ...

Not broken just different. Sometimes very funny You can easy try it in a emulator.