Yesterday was a good day.
I went to a friend of mine and first of all we did the
harness upgrade (so that I could run V5 maps):
Then we swapped cylinder 5, 6 spark plugs and coils with the ones of cylinder 1, 2:
The plugs were in great condition:
Then I uploaded new firmware and Rev.2a V5 7-29 Upgraded Turbo MT maps (followed all the instructions in the readme file) and went for a spin. I did 7-8 WOTs and the misfires were gone! I wanted to do some more testing and data logging, but the roads were damp and it was really scary

I even managed to spin the tyres @ 140 km/h (~87 mph)

Vishnu autotuned from initial 15 to 17 PSI in just 3-4 runs, so I believe 17 PSI on pump gas is not the limit

I'm not sure if it wasn't a placebo effect (didn't have my Pbox with me), but the car pulled significantly harder. I'm starting to love my RBs!
It is a bit too early to make conclusions, but most likely the misfires were not hardware related. Most likely it was either V4 fimrware/maps fault or incorrect firmware and map uploading procedure which was a result of absence of readme file.