It's a very, very easy answer, but you're asking the wrong question
The question you
should be asking is: "Why do I
want it to be a 60A circuit?"
I have mine downrated (and placarded
) to 30A. Why? Because I go to sleep for 8 hours every night and that's more than enough time for a top up at 30A
I did it after doing a load calculation (did you do one?) but also the lower current is just easier all round on the equipment
So unless you're driving a taxi and need to be constantly charging back up and/or have to get it done ASAP, forget about running at 60A