tyre question.

[Grahamm]

Question is, will 300 miles of motorway "square off" the tyres?

Simple answer: No.

If you do a few thousand miles of motorway type riding with no twisties then, yes, they'll start squaring off (how long this takes will depend on your riding style), but a few hundred miles won't make a difference.

You'll probably get lots of recommendations of the "best" tyres to get, but any good dual compound tyre should cope with this sort of thing and not require replacing too frequently.