Since the mid 80’s I have used Metzelers on a variety of bikes: RD350YPVS, FZ750, VF1000 and YZF600R. Generally an excellent tyre and price is OK. Just make sure you have a matched set Front and rear if possible. On my VF I had a Metzeler on the back and a Bridgstone on the front. It didn’t handle at all well.
I don’t think Metzelers are the ultimate choice for a big sports bike, but for the GT750 they should be excellent.
Good bike the GT750, bounce well…check out my post Six of the Best in the Crashing section!
Let us know how you get on with the tyres. Life, feel, grip etc.