Alan - Coming from Koamaru we go between The Brothers and Arapawa Island then almost always between The Brothers and Awash Rock as you say. Can get some very steep seas south of The Brothers though in heavy conditions so occasionally we have gone just south of Awash Rock before heading across but never as far south as Perano Head.
Heading across I normally make my mind up around Awash Rock area whether am going to go round bottom of North Island in close or 3-4 miles out (3-4 miles out decided this far back does not make a tremendous distance run difference, but certainly makes a big difference if you get between Terawhiti and Karori close'ish in and then find it is wiser to be 3-4 miles out
I find from Awash Rocks heading towards Karori the perspective is quite deceptive due to the roundness in plan of Cape Terawhiti and is visually hard to get the best heading and chart work is complicated by the tide which varies alot going across, even backing in places as it eddys. So very easy to end up much closer in on approach to Terawhiti than planned (I think that is what you found). Whichever way one is going one has to allow much more than one thinks for the tide, but is complicated because it is so unpredictable both in terms of time, speed and place (including back eddies).
Going across Karori Rock to Sinclair, if possible in lighter conditions the best ride is generally very close in (but watch out for Thoms Rock) but can be dangerous if there is a biggish southerley swell as it can look calmish but then some quirk of the tide or something starts the swells breaking a mile or two out off Karori - not something to get caught in. It is also pretty much impossible to know what it is going to be like until one gets there.
So, most times now I just set myself up from around Awash Rock to be 3 or 4 miles out at Karori. It is pretty much impossible to do that and maintain it though unless one has an electronic charting system and can monitor
all the quirks of the tide on the way to Karori. I have forgotten the extra distance as opposed to going close in but as I said before as long as you set yourself up way back as you come through between The Brothers and Awash Rock it is not great compared to being forced into doing it when you get there.
All that is very well if one was not a sail boat because the wind
is usually not kind to ones best laid plans - so we stick to the above plan including keeping to time by not being shy of motoring whenever best to do so and most others do the same.
EDIT: Coming round bottom of North Island the wind
can be easily twice that forecast
for the Cook area - a pretty good indicator of the wind there is the wind speed on Mount Kau Kau given in the weather
reports. Although well inland and elevated so seemingly not related at all, it seems to have similar wind speed.