3" and 165kph of pure Shonk! 
Had a lot of fun putting this together, and loads of the usual FPV self-build frustration including 3 total rebuilds, 2 rinsed batteries and 1 fried FC. (No partridges though) Still.. better than being bored.
This is my version of a 3" design I saw online and is a dinky version of @Cedric 's current record holder. Never gonna touch that, but for a 3"… I’m chuffed with the results thus far.
Using an iFlight Blitz 7 FC with 55A ESCs (after I toasted a smaller board 
) and 3600kv motors. It’s not quite sub 250g once you count the Vista set up and the battery. Have hammered it on 4S, and this is probably as fast as it goes. I put the pitch angle on the OSD so I could actually see how far over I was as it’s damn hard to judge accurately and I didn’t want to plough the field at >150kph!
The base set up..
All packs neatly into the rocket body.
It’s sooo shonky! 
But… it shifts too…
Not sure of the exact rules of this game.. so here’s a screen shot of the bbl file..
Maxed at 45.82mps - which Google tells me is 164.95kph. Which I’m blummin pleased with!
I also have a 6S that I will try next … gently at first. It shouldn’t fry anything but it actually flies really nicely now!