27's will fit with no lift, if you want a mud tire I would go with outlaws or mudzillas. Mudzillas are going to ride smoother than outlaws, your foreman wont have any problems turning them.
The warranty is up to you, some buy it and never use it, some use it more than enough to justify the purchase. It pretty much depends on how you ride, also make sure you think of future plans for the the foreman if you have plans on adding things that might void it then why bother. I bought one with mine but will only use it for big fixes, it is just too much trouble to put it back to stock and then wait forever for them to fix it when I can do it myself and fairly inexpesively. Also check out your local shops, some of them are a pain to get anything covered under warranty.
The warranty is up to you, some buy it and never use it, some use it more than enough to justify the purchase. It pretty much depends on how you ride, also make sure you think of future plans for the the foreman if you have plans on adding things that might void it then why bother. I bought one with mine but will only use it for big fixes, it is just too much trouble to put it back to stock and then wait forever for them to fix it when I can do it myself and fairly inexpesively. Also check out your local shops, some of them are a pain to get anything covered under warranty.