What calipers have you got? Are you going up in front disc size as well as the multi-pot calipers? My recommendation to you on pads would be the peerless Ferodo DS2500, best pad I've ever used. Also get a decent fluid in there, I always swore by ATE Super Blue, superb stuff - high boiling points, but also not particularly hygroscopic.
I'd say that upgrading the back brakes gives you far less significant brake performance gain - you get something over 70% of your braking force from the front wheels, so that's where you'll see the best improvement.