Difficult question, and one that can really only be answered by yourself, but here's my thoughts for what it's worth.
As I'm sure you already know, the main differences are a 4" bigger throat, front mounted quick tensioner, quick clamp and two spare clamps. While I personally don't think the differences justify an extra £240, if I was buying first time and buying new and had the money, I'd want the extra 4" throat. In 12 months of owning my Hegner, a 14" throat would have defeated me a good number of times whereas the 18" throat of the M2 has only been a problem a couple of times. As for variable speed, I don't have it on my M2 and don't need it, but if I was a first time buyer and I could afford it I would have it, especially if I was a beginner. There's no denying the extras of the M2 are good to have, but the M2 with variable speed is double the price of the basic M1 which is still a very capable saw. I think it's all down to what you can afford, so go for the best you can afford.
You could always go for the Polymax3 and pay an extra £1000 for the privilege of changing speeds manually. :mrgreen: