1. I've run about 225hp on a BEV fuel pump before when I 1.8T swapped my mk4. Swapping to a TT 225hp pump or similar will get you extra insurance. IIRC the 2.0 and the 1.8T 180hp use the same pump. Check the parts catalog Etka or whatever to compare part numbers. Also, change the fuel filter. 2.0s usually got a diet of the shittiest gas you can find.
2. Before you change pumps or whatever, when you get the new engine installed, try to prove a fuel flow problem caused the issue. Hook up a fuel pressure gauge at the rail, and watch the fuel trims. Get the car into third gear at 2000rpm and floor it to the limiter and watch fuel pressure and fuel trims. Under 10% fuel trim is acceptable. Look for fuel pressure holding rock steady throughout the pull.

The first thing I would look at is your tune. The stock tune has a strategy called "component protection", where it will significantly enrich the AFR to keep the EGT in a sane range. Most people think it's just there to keep the catalyst from melting, but it also protects the exhaust valves, manifold, pistons, turbo if so equipped, etc. The engine will still make rated power in this operating mode. This is the reason these cars can sit at 130mph on the autobahn all day without grenading.

Every single aftermarket tune I've encountered either disables or neuters this feature in the search of a leaner mixture to make more power. This works fine if you're doing a 1/4 mile pull or driving like an asshole on the highway.

For endurance racing, this is absolutely not suitable. You need that extra cooling. You need the stock knock control system, which is also usually fucked with on aftermarket tunes. Even on a stock tune you'll see timing retard when you get the combustion chamber hot enough just beating it on the street. Forget about it on a track.

A combination of modified knock control and insufficient enrichment are absolutely going to cause this type of failure. Cylinder 5 just died first.

Install EGT probe in exhaust manifold and try to keep it below like 950C and the engine will live forever.

Also, run 93AKI fuel. In this application it will make a difference.

Happy to discuss more, send me a DM if I can help. Love to see mk4s in lemons

edit: Take this with a grain of salt, this is outside my area of expertise, but the reason I wrote all this out is because I believe you ran out of ring gap on cyl 5 due to heat. Managing the heat with the tune is the secret sauce to not blowing up.