I'm probably more likely to be throwing a small tungsten nymph or two than tiny dries and I'll be taking it to NZ as soon as I can negotiate some man-leave.
in that case i'd take the SLX as main line for your nymphs and maybe more for the more-than-probable wind and the Smallstream on the spare spool for when you need to cast the lighter stuff.
this is exactly my setup. i'm not in NZ but i live in a long valley that goes from the Atlantic to the Mediterranean and there's always wind, often very strong... from one side or the other. the SLX handles bigger or heavier flies better and does much better in wind.
inversely, the SS is better at smaller/lighter imitations and tends to give gentler presentations.
with both you have the best of both worlds on an awesome rod
cheers,
marc