I use OS4.1 with WinUAE on my i5-Laptop.
The latest beta doesn't freeze anymore, it is useable. With the correct configuration it runs stable.
For my purposes (using small native programs, getting to know OS4.1 better, programming in Hollywood..) it is fast enough.
But if you would like to use it for demanding games or ports of big linux software, then it is to slow.
A few weeks ago Amigakit was the only vendor who sold Amiga OS4.1 Classic, I don't know if this has changed.