Not sure if you are looking for new pups or not... but for metal you want humbuckers - rhythms off the bridge and mix the leads up between bridge and neck. Depending on the sound you want, I would suggest with Dimarzio Evolutions or EMG 81/85. I've had a lot of guitars over the years and my consistant favourite are the Evolutions. Try them out on an Ibanez Jem in the local store (make sure its the white one with the vine inlay - other models use different pups). The 81/85 combo is pretty popular too, you should be able to find them easily to test run too.

As far as using the pups goes you get less output from the neck which makes it more suitable for sweep picking, you get a creamier blues tone from that setting too. THe neck generally has the highest output and the clearest tone accross the range - this makes it good for rhythm guitar (less mud) and screamier leads.