Have you tried to multi box millions of these scripts at the same time? and have them in cahoots with each other so they don`t try the same key 
If you had slush pools cpu power it would not take long you could probably run a trillion at the same time and if they are storing used keys to a blockchain or data base, it will cut the time down by a shit load.
If you had slush pools cpu power it would not take long you could probably run a trillion at the same time and if they are storing used keys to a blockchain or data base, it will cut the time down by a shit load.
It's been done.
https://bitcointalk.org/index.php?topic=1877935.0
https://lbc.cryptoguru.org/trophies
It has found several keys in the (very) low range of 256 bit integers, but to search the entire space is essentially impossible.