Seems a bit daft - if this turns into a race, I suggest you take your bikes to Cadwell park or something ! suitably twisty demanding circuit.
The Fazer 1000 is a good all-rounder, with the R1 motor and front end, but in a package which can be had new for £6K - but its horses for courses - I would hope that a Fazer could see a GS off in some circumstances - with 130-140hp on tap and a superior power to weight ratio.
But, I would contend that any reasonable bike of 500cc plus or 50bhp plus should keep up with any sportsbike on real twisties - it's like saying a Porsche 911 could leave a well-driven Focus RS or Honda Civic Type R for dead on the twisties - it ain't gonna happen, because the Porsche will rarely get the chance to exploit its superior power to weight ratio.
Rather than risk your life proving a point, just ask your Fazer owning mate these questions:
1) What will the finish on his bike be like after one bad winter
2) Come trade-in time, how much value (as a percentage of its original price) has his bike retained
I think you'll have the last laugh.
6X