https://marketplace.tf/items/tf2/30039;5;u76 - Sold for $140 when Keys were $1.89 each (74 Keys)

https://imgur.com/a/GsCTAlw - Capped by the buyout of 60 Keys

https://backpack.tf/profiles/76561198142110950#!/compare/1589587200/1589673600 - Sold for 70 Keys

https://backpack.tf/profiles/76561198275735463#!/compare/1589500800/1589673600 - The Crone's sold for 77 Keys; 7 not used

https://backpack.tf/profiles/76561198169916882#!/compare/1589587200/1589673600 - The 77 Keys

https://backpack.tf/profiles/76561198275735463#!/compare/1590278400/1590364800 - Better for the Burning Tyrolean

https://backpack.tf/profiles/76561198824740252#!/compare/1589932800/1590019200 - Sold for 60 Keys

https://backpack.tf/profiles/76561198074992626#!/compare/1590019200/1590105600 - Added 5 Keys for a CV Timeless Topper (being used there)

https://backpack.tf/profiles/76561198203205792#!/compare/1590796800/1590883200 - Can't tell the full sale

Sale 2 was the Glove + PE Slouch for the Burning DCO + 10 Keys. That's probably better to drop the DCO.

In Sale 3, the G. Fetti Yellow Belt was added to the Connoisseur's and the PE Slouch was added to the Glove. This sale is still better for the Conno anyway.

You'll need a picture of Earl's 68 Key sale to use it since they don't appear on either side's compare, but it fits in the range even if you don't get a picture.

Since 65, 68, and 70 each took a day, I'd call 58 low. You can go 60 - 70 Keys here.