Optimas are also known for being very vibration-resistant. Vibration/shock can kill a 'normal' battery pretty quickly. Optima's are (or were, been a while since I was more involved with that culture) a battery of choice for serious 4wd off-roaders for that reason and the non-spillage. Seems appropriate for a tractor as well.
Add in the fact that my red top will spin my Jeep starter at zero degrees F like it was 70 and they are IMO a no-brainer. I've heard of some issues with QC on some red tops but haven't run into any personally.
Tim