350kms, that's awesome.....my record was 206.8kms for the F100....
The big question here is what sort of driving is it, 350 is no good on the highway, but not too bad for stop-start in traffic. I aim for around 350 - 400 around town and 600ish on the highway, that's on 18psi.
I have an EBC these days and it makes no discernable difference to the fuel economy.