It's very possible for an A6 motor to have 450whp. Especially on that much boost.

It is VERY unlikely that:
1.) He was running pump gas
2.) He had a stock head
3.) He is really running that much boost, or making the numbers that he was claiming.

Now, to the guy who was told 800whp with 800cc injectors.... that's not correct. He would need like 1100cc injectors to make 800whp. Much more then 800cc at the least.

It's not uncommon to find a 450whp SOHC motor in the US.
It is uncommon to find one around this area. More so, to find an A6 in this area with 300+whp.