Sorry to hear about your FZS600, sad that another classic goes to the scrapyard due to thievery.
Bought my Fazer 8 back in 2020, paid £4250 for a 14 plate minter with low mileage, Givi rack and box, heated grips and gear indicator fitted too.
Came to this from an SV650 and was so impressed at the build quality, power and finish on the bike. Can't comment how you would feel coming from the FZS600, but I think you'll like it?
Have original rear shock on mine and have to say I have no complaints about rideability or comfort, but then everyone has their individual tastes.