The original Hawk has a 2.5 mm stroke and the Hawk Spirit has a 3mm stroke The thunder has a 4mm stroke. I have been using Cheyenne products since the release of there condor in europe, i currently own all of Cheyennes machines. I will say that Cheyenne really makes some great stuff ive had my original Hawk for almost 4 years and no problems with the motor yet. Both the Spirit and Thunder are amazing machines both are versatile in every field of tattooing. The Thunder has a more powerful faster motor if you own an eikon ems 400 then the thunder will work fine without the startup cord otherwise you will need to purchase a startup cord. Cheyenne is doing really great things as Jeff Gogue has recently joined the team along with Jess Yen. Next year i heard they will be releasing a wireless machine. I have tried many other rotary machines from Stigma to Dragonfly, bishops, neotats and many more all of them being good machines they just dont last as long as a Cheyenne machine.