I know as a beginner that BLHeli_32 lets you run DShot1200, while BLHeli_S can do DShot600 at most.. But apart form that are there any other differences in terms of performance?

BLHeli_32 is smoother, especially with 48khz FET PWM, and _S tends to feel sharper.

I actually feel like _32 seems a tad less direct, but you can recover that some by using feed forward and tweaking your rates a bit.

There are other differences that are more technical in nature that I could go on about for a while, but they're more academic than functional.

Telemetry and native dma for DShot are excellent additions, but don't really impact flight handling, more a convenience thing.

Also the difference is pretty small even in flight handling, so I would say a large segment of pilots are probably not at the point where it would make a difference or they would necessarily notice.

For certain types of flying though it's quite noticeable.

Most importantly you can now play music with custom startup tones!

But seriously, currently limiting seems like a great addition and I'm surprised from ESCs don't support it.

Not all performance related, but some advantages of BLHeli_32 over BLHeli_S are listed below (taken directly from Oscar's blog post HERE so all credit goes to him)...

• Programmable PWM frequency of up to 48KHz
  
• Auto-timing for higher efficiency and realiability
  
• Current limiting (with built-in current sensor on ESC)
  
• Adjustable “Brake on Stop” force
  
• Improve direction change in Bidirectional mode
  
• ESC Telemetry
  
• Configuring from FC using DShot commands
  

And another of Oscar's blog posts on the subject worth a read is at the link below:-

https://oscarliang.com/best-blheli-32-settings

Blheli_s is open source and written in Assembly. Blheli32 is close source written in C++ by the same people who developed Blheli_s. If you buy blheli32, those guys get paid for their time. Blheli_s has pretty much stopped development. Blheli32 is the current and will continue to be supported.

As far as real world differences, I can't tell.