Wouldn't be surprised seeing as Booker is old but he's still crafty as hell. I'd say it's 70/30 that Booker gets stopped.
Yes, if he convincingly beats Booker. Then Hrgovic should step up to a top 20, maybe top 10. Lots of choices, some have already been mentioned.
I think that might be a very good fight. But looks like too early for Hrgovic. Not sure Whyte wouldn't take it. Whyte might be soon getting into a bind. He's still relatively young for a HW, but before long will be near mid 30s. He needs to position himself for a title shot sooner than later. Getting KO'd by 40+ year old Pov has set him back. I'd like to see Whyte vs Willder. Lots of resentment from Dillian - justified - against Wilder. But Wilder's latest ramblings are putting off many in the boxing business.
Him beating an old Booker doesn't really prove anything. But having said that he's ready to step up. Don't think he should step up all the way to top 10 level opposition, he could beat some tip 10 guys probably already but he could also lose to some. I'd like to seem him tested by facing either another prospect or gate keeper type heavyweight. Not really a great idea to step up from fighting journeymen to fighting top 10 guys straight away. Chisora has been mentioned and he'd be ideal, dangerous but a proven litmus test at heavy, but I doubt Chisora whose been facing big names could be offered enough to make him interested even after his loss to Usyk, he probably has better options as he's still marketable in the UK and capable of making some decent paydays still which I doubt Hrgovic can provide. Maybe a fight with Ajagba. He's been let go by his former promoter, he's got fewer options than before and so could be a viable option and it's a fight I think Hirgovic would win and look good winning, with Ajagba being open for the right hand, I could see Hrgovic crushing him in impressive fashion.