rotosounds but steel strings will more likely be the right choice for you.
No way, they sound dead straight out of the packet - even steel.
D'addario steel strings are great. I like Ernie Ball steel too. Very clanky. Remember to set your action overly low if you want brutal clankage.
Not to hijack the thread, but what gauge bass strings are people using for lower tunings? I currently have a rotosounds 50-110 on Ibanez SRX set up for drop c (C G C F), but is there an advantage to going heavier gauged than this? Looking at prosteels, there 50-105 set seems to be there heaviest 4 string set.