Thought I’d give the Beach a go and try some of that sea breeze, which there was absolutely non of, not even a flutter. So was lucky to achieve this speed really.
“Life’s a beach and then you fly.”
That’s pretty much where I was. There was no breeze on that day. Not that it helps you, did you fill it up with coal before you took off?
Try with a 50% battery - it will be lighter at 50% - fewer electrons.

Haha this did run through my mind 
now I’m thinking really long tunnel forcing it into atti mode
You won’t get the GPS reading for the speed underground

Ah shit! 

Are you only flying forwards? Is there any chance that it’s a little faster (for whatever reason) in reverse?
Try Box Tunnel, you might get some Intercity 125 help
Get High and fly down the gravitational pull will give you that bit extra! 
I think that’s called “SPLATTI” mode.
GPS speed is horizontal only - and it’s GPS speed limited. Slopes achieve nothing.
Get one of the guys to 3D Print you a ‘Mini 2 Holder’ that you can attach to the roof of your car Steve 
Get Somerset to join the 21st century … if you’re flying at the time it catches up you should get warp speeds. 
Does GPS speed work by recording time taken between to points, let’s say A and B, so if you fly slightly vertically down wouldn’t the two points be slightly closer together? and the time be slightly quicker! plus the gravity effect! might be worth a try 
It only looks at horizontal coordinates.
Vertical fixes on GPS are notoriously flaky … I’ve got a GPS track in my car that was 150ft below the road, others below sea level.
In fact, they are so flaky, if it was logging 3D speeds I’m sure Steve would have broken the sound barrier by now.
Also - check the speed displayed whilst your drone is climbing/descending vertically. It’s 0mph … and the vertical speed is shown separately.
Vertical distance/speed on DJI drones is all done barometrically.
Would turning off the engines at 400 feet help with speed?
Only vertical speed - see last post.
Think I just need a super blustery day. All my attempts have been on dead calm days.
Try in reverse, too. I can’t recall which direction, but my MP is a smidgen faster in reverse or a diagonal angle than straight forward.
I think that’s to do with pitch/roll limits that aren’t measured identically in all directions.
Could try flying a circle with the right stick and not changing heading on the left stick. That way you try all relative headings.