To be fair though, I love all things Volkswagen and have owned two beetles, and did my driving test in a new beetle. They are great cars and go pretty hard. The federals will increase the handling on it, but I would also look at suspension, it's pretty soft, and can affect cornering a bit. I'd just go with 535s though, for an NA Beetle. I would have used 595s on the turbo version.
Obviously your call, but my input as a Volkswagen and federal user