Bandsaws are often talked about in terms of wheel size , 12", 14", 16", 18". I think your 315 is a 12" model. Charnwood tops out at a 14" model. Record 300=12, 350=14, 400=16, 450=18". I upgraded to a 430mm/17" model a year or so back and find it a good sized machine for both small and large tasks in the workshop.
My old band saw, was a 14" model with a 750W motor was under powered, personally I'd not go for a bandsaw with a motor smaller than 1.5kW.
I do not use the blade tension indicator, I don't think they are particularly useful, I prefer the 'Carter' deflection tap test.
For that sort of money you may also want to consider a second hand machine, you could pick up a Hammer or a 5yr old larger Axminster. Although delivery/collection often becomes the issue.