Has the Sierra Pacific line done approved testing in NZ? I recall the Plygem did do thorough testing requirements via BRANZ so local city councils will have no issues on using their windows in NZ. The greatest problem NZ has in building is the red tape / regulatory requirements forced on the industry because of a bad experience of untested overseas products AND methods were tried in NZ some 20+ years ago and because of the slack regulatory building code back then, it allowed the development of NZ's leaky house syndrome. Keep in mind not 1 single factor was at fault but the mix of overseas materials, overseas methods, lack of local understanding of these products, lack of how they would integrate under NZ building ; is what led to the leaky house mess we have today. So the issue is the "building SYSTEMS that differed". For eg. NZ houses are still passively ventilated vs N. American homes for many decades have gone on to HVAC active ventilation. NZ houses are built with passive solar in mind while in N. America, houses are built very close together with little or no consideration to solar orientation. NZ acceptable building code requires walls to breath while in N. America, particularly in places like Canada, the use of a 'vapour BARRIER' is required and indoor air quality and moisture is managed via the HVAC system. Vapour barriers are not allowed under NZBC for this reason and the cost of energy in NZ does not permit houses to have such HVAC systems in residential use (well it's ultra costly). So regulatory councils today realise that there are differences in these building systems and without any formal NZ testing, or someone you could pay a lot of $ to vouch a producer statement to exclude the product, local regulatory building councils will not accept.
As much as I prefer the N. American vinyl windows, i'm burdened by the high restrictive regulatory requirement in NZ and as you know, if no house gets a 'Code of Compliance' certfiicate, then the house is basically worthless and un-insurable.
On a window note. Our home was built in 2009 with the Homerit uPVC window extrusions. The SGU glazings were installed after the window frames were fitted in the house. The SGU were high spec double pane, Low-e, with plastic spacer edges, (no argon because they leak) by Viridian Glass. I'm disappointed that nearly 1/3rd of these SGU have started to haze on the inside in early morning which indicates to me the SGUs have lost their seal. Perhaps the earthquakes where we live in Chch is the major cause, but i'm not seeing such response of lost seals in conventional glass used in aluminium framed windows.
Oh and another thing, N. American vinyl windows typically have PVC around the window reveals instead of timber reveals that is used for NZ windows. Also there needs to be attention to detail of the window offset from the wall framing as this will affect the reveal width, particularly homes that want architraves around the windows. So more often i've found imported windows seem to omit the reveals to allow for such variations but IMO, the end result is an inferior product. If you're going nail find extrusions, you best be sure the architect knows how the window will sit inline with the wall insulation and how the reveals will adapt to the interior design.