Well, I'm a "practical" kind of fellow. I've already riden 1000s of km on gravel roads already this year with my cast wheels. But I actualy own three sets of wheels. Two cast and one spoke. Cast wheels are definetely more rigid and handle better on paved road.
They actualy handle better on unpaved road as well. Much more rigid than any spoke wheel. The problem is if you hit something to a point that they will bend, they are barely reparable. Spoke wheel will actually break before a cast wheel. But it is reparable. And if worst comes to worst, you can change the rim.
Also, spoke wheels requires some maintenance once a while, but not too often.
Finaly, cast wheels can be found everywhere on E-Bay for a much cheaper price than spoke wheels. If you intend to own both cast and spokes, it is better to buy the bike with spoke ...
...I would keep the spokes simply because they are a £260 option that you've clicked for free. If at some point in the future you decide you really want cast, I'm pretty sure you'll find someone on here willing to swap plus some cash your way.