Upgrade Program or Upgrade Contract? (UK)

So I'm with Three at the moment and my contract is up for early renewal next month.

I'm happy with their 4G coverage and they haven't given me any issues in the 2 and a bit years I've been with them.

I've got the 6 Plus and it's served me well. I'm looking to get the IP7 and can get the 128gb version for £51 a month (making a saving of £5 each month to what I'm paying now) on another 2 year contract.

But with all these rumours swirling about next years phone, I can obviously try and get on the upgrade program, and see what happens next year.

So that would mean bumping down my tariff to a SIM only one, then paying the monthly payment to Apple, which would then work out to what I'm paying in my current contract.

So I guess my question is do I just upgrade with Three and sign on for another two years, or do I attempt to get on the Upgrade Program (with no guarantee that I get on it (I've seen people here saying they've got perfect credit get declined))?