I would suggest a 1600-1800mhz kit, because as you said, you want it for 24/7 use.. Some from Corsair or OCZ should be great, and also they have great oc potential, especially some Corsair kits like this, or if you can afford, Dominator should be fine...

I wouldn't suggest a kit at 2000hz except if you are interesting on extreme overclocking, then see some CSX kits that have D9GTR chips, or Cellshock, especially the one with the blue heatsinks at 1866mhz..they are just great, but unfortunatelly extremly rare