59.1% - 69.8%
With Adamant: 64.8% - 76.9% Still a 2HKO
With Adamant and Life Orb: 84.7% - 99.6% chance for OHKO with Stealth Rock. For sure OHKO with three layers of Spikes.
With Adamant and Earth Gem: 97.5% - 115.3% Very good chance to OHKO, for sure OHKO with Rocks.
The lesson here is how important entry hazards are to netting KOs.