Something else comes to mind from reading your posts:
- Once you are living in NZ, where will most of the websites you access be located?
- You are focussing on Sync. Speed so much that it worries me, because in most cases, this will not be the determining factor as to the quality of your internet connection.
- If you are expecting to be able to access streaming video from the UK once you are in NZ, be prepared for a big disappointment. It will most likely work (so long as you have an account with a provider who doesn't try and enforce IP range restrictions*), but the maximum speed you will get will be something like 500kbps at peak time (evenings or weekends) or maybe 1 or 2Mbps during off-peak hours (weekdays).
- The reason for this lack of bandwidth out of NZ is due to cost. There is currently only one fibre ring connecting NZ to the rest of the world, and it is owned by a monopoly. Consequently, most NZ ISPs purchase the minimum bandwidth they can get away with, whilst not getting too many complaints from their customers. Hence, the evening slow-down phenomenon mentioned above.
- Maybe you are aware of all this, but I thought it prudent to mention it because of the extreme importance you are placing on sync. speed. In practice, a few extra Mbps at your end will make no discernible difference because of the bottleneck formed by the international pipe out of NZ.
- If you are into Bit Torrenting, you will be able to get more out of your connection, but no matter what you do, I doubt that it will be possible for you to get much in excess of 10Mbps of International Bandwidth, aggregated over all concurrent processes that are running. This is a bit of a wild guess on my part, because I am not a torrent user, but from what I have seen, others were managing to max. out their connections to around 5 or 6Mbps of torrents some time back, so it seems reasonable to assume some increase has taken place in the meantime.
If you can provide some further clues as to the categories of your expected usage, and the geographic locations of the servers they would be coming from, one of us on this forum can probably give you some further guidelines as to what you could expect.
* Due to IP range restrictions, it is not possible to access BBC iPlayer content from NZ. Maybe you can get around this by using a VPN leased from a UK host, but I haven't tried.