The time is 10 hours, but I do believe the seats on the Thomson flights are 33inches leg length, so you really don't need to upgrade. You will also I believe have complimentary drinks. Coming back it is always quicker because of the trade winds.
More room, better food, bigger luggage allowance,
We have just flown back from Quebec to Gatwick with Thomsonfly and could not fault it for legroom, comfort and service. There is no need to pay for an upgrade in my opinion...save your money for the cruise and enjoy!