Do I need a tourer or can I get away with a road bike & backpack for a week away?

This. Definitely.

I would (and did) look at Kinesis. They have a good rep, a few on here have used them for racing, very practical.

If you're touring in the summer, you can use 28c without mudgaurds (or maybe clip-on's), plus a rack.

A older 105 tripple groupset: Campagnolo, Shimano and Sram Groupsets - Merlin Cycles

This.

A couple front pannier bags on a small rack, together with a stuff bag strapped to the top, will give a nice amount of load capacity.

http://www.fatbirds.co.uk/5789/products/kinesis-racelight-tk2-road--aduax-bike.aspx

I have been lusting after this Spa cycle Ti Audax for quite some time. If you're not camping this thing will do everything.

http://www.spacycles.co.uk/products.php?plid=m1b0s21p2573