Problems with rising sponge in larger tin For years I've made classic 6/6/6 and 8/8/8 Victoria sponges (and many variants) in two 7inch tins, with good results.

Now I've tried to bake the same recipe in one 8 inch spring form tin, and had to almost double the cooking time as the centre remained uncooked. Eventually the middle was still moist, while the edges were almost brownie-like in texture, and the cake hadn't risen much at all.

The same result occurred with damp towel around the tin edges, to even cooking pacing, and extra baking powder, so I'm concluding that somehow either something is fundamentally wrong with my approach, or the tin is cursed. Any insight would be much appreciated.
I see nothing wrong here. The two 7 inch tins have a total area of almost 310 square inches, while one 8 inch tin has a total area of 200 square inches. So your batter is 1.5 times thicker in the one tin. 

Baking time does not increase linearly with thickness, so a doubled time is not out of the ordinary. Time is not a prescription in baking anyway, you have to bake it until done and not until the timer goes off. 

The "hard on the edges, gooey in the middle" is a classic sign of too high oven temperature. Reduce the temperature to bake the thick cake. 

Alternatively, make only 2/3 of the batter, or find a 10 inch tin (314 square inches area).