Sure scrapebox works fine for this, and I use private proxies and I can check PR all day long, you just have to do it right.
The IP bans come from too much too fast. So if you set your connections to 20% of your proxies it works great. Meaning if you have 50 proxies set connections for PR checking to 10. If you have 10 proxies set your connections to 2.
The problem with using public proxies for PR checking is you can PR check the same url with 3 different proxies and get 3 different results, private proxies are consistent.
I have PR checked hundreds of thousands of urls in 1 run with my private proxies without a ban by using the connection settings above. If just allows enough time between when each proxy is used that it doesn't trigger a ban.