Hi, I've grown Thai Basil Siam Queen (not a Sutttons one) and was pleased with the flavour and yes aromatic, slightly aniseedy, and definitely the thai basil flavour you want, but as to strength of flavour I'd say it was fairly mild.
From what I know (not a lot!!) there are a number of different types of Thai or Holy basil, the leaves can be different shapes, bigger /smaller, darker /paler, and yes the flavour will differ. And as goodlife says, growing condictions will affect the flavour. I guess it's a matter of trial and error! And whether we have a good hot summer.
let us know how you get on, and if you find any particularly good varieties or sources I'd love to know :)