I'd take the 58, that's not a fluke. You can golf your ball if you're going that deep. Majors have been backed into and lost only to find first and only time winners.
That's tough because there is more than one way to win a major- outright beat the field or have a couple players step on land mines and hand it to you.
Shooting the first 58 in tournament though is something done entirely on your own.
I'd take the first 58 on tour over a major. Any given major is won every year who knows when or if 58 will be done again