Re: Looking to purchase a new Guitar
As you said used Prestige is the sweet spot for sure where you get good pricing for the good Ibanez stuff that someone else has possibly barely used. My advice is to choose body shape & then make sure the bridge meets your needs - if you only want an Edge/LoPro/Pro trem look for those whereas if you don't mind the EdgeZero that gives more choices. Some Ibanez fanatics obsess over the neck dimensions but to me that is often splitting hairs.
Your location is not shown but £600 is not here so what used availability is in your region is another story. In the USA Prestige Ibanez litter the market (in a good way) it's amazing people have so little regard for them and will pay sometimes 2x for indo Ibanez with grossly inferior tremolo, wet wood, etc. Good luck.