Hi Sam I would urge you to stick with it! It is amazing how much work you can achieve in a short time if you are determined. You sound like you have got your project clear in your mind now and with the results starting to happen, it would be a real shame to quit. I'm in the process of finishing my analysis and writing up at the moment and for various reasons, things are only really starting to come together now.
If you are pushed for time or feel that you might want to move on to something new, why not talk to your supervisors about submitting your thesis for an Mphil instead? I just think it would be a real shame to walk away with nothing after 2 years and you might regret this later. All the best.