Brake upgrade or pad upgrade?

I am looking to replace the pads on my brakes before I go off on my JOGLE. However, as I have Sora brakes, do I upgrade the front to a 105 with the stock pads for about £35, or change the pads on the Sora front for Swissstops green for about £25? Will the 105 brakes actually provide any extra feel or power, or should I just upgrade to Swissstop holders and pads? I'm erring towards the holders/pads as I can't imagine that the callipers make THAT much difference... :?
I don't have the money at the moment to change to 105 AND Swissstops, as beer funds for Lands End are rapidly dwindling....