Yes, they're some of the best options available to a DW DK outside of raids. The other best option outside of raiding being the Black Icicle from H HOR.
Nerubian Carapace should be your runeforge of choice for the effective health. If you're using them for farming heroics and not ICC, you might be able to swap to a threat enhancing runeforge just to help yourself out in the AOE fest that is the 5 man. Those axes drop so frequently you might be able to carry around several of them with different runeforges and swap them out depending on your needs.
Cool, that was my thinking too. I was using a mix of Rimefang's Claw and Peacekeeper Blade but since I'm def capped before taking weapons into account the fast/fast thing didn't make sense from a threat perspective. The expertise on the peacekeeper was nice though.
Dual Black Icicles would be better imo just because armor pen doesn't do a whole lot for Frost and the hit would be better. However there's nothing wrong with using Nighttime and at least you have the sense to use dps weapons for threat unlike some DK's. I use Black Icicle and the 1h mace from Anub ToC 10 man, the socket is nice for a stam gem.