While doing our research for this passage it seemed that there were two main approaches:
1) Sail the rhumb line
2) Sail more Westerly than the rhumb, taking advantage of the NE trades, at some point between 125W and 130W cross the ITCZ by heading directly South until we reached the SE trades and then point our bow at the Marquesas.
As major ocean crossing newbies, we took the expert advice and opted for #2. All of the while in the back of my head was a disturbing bit that I read from Don Anderson in which he said that while he advocates #2, and that while having a strategy is good, that crossing the ITCZ is a bit of a crapshoot for two main reasons:
1) The ITCZ can move hundreds of miles in a 24 hour period and often does.
2) No one can predict its movements.
These are two very good reasons why two boats leaving within hours of each other (but traveling at different speeds) can have very different passages. The ITCZ is a slippery bugger, and as we can attest, it can bloat up like a puffer fisher and become a big diffuse wind and convection blob without a coherent zone as its namesake suggests.
How can we attest that? Well, we kept feeling like we were in and out of a watered down ITCZ. We had sudden increases in heat, humidity, and convection and light flukey wind that came and went - for 10 days and many miles. We had already noticed that on our weather downloads the ITCZ was being represented in multiple sections rather than one continuous line and those sections were separated by hundreds of miles, both N and S of the Equator. This made us suspicious enough to read the footnotes on the text weather forecast which told us that "the convection activity was not sufficiently concentrated to make a reliable statement about the location of the ITCZ".
Woah. Not only does it move, and we can't predict its movements, sometimes we don't even know where it is RIGHT NOW.
We left very early in the 2012 season and perhaps that influenced our experience. One weather guy backcasted* that "sometimes the ITCZ does this at the vernal equinox". Or maybe it had nothing to do with time of year and was just one of the many weird things the ITCZ can do at any point.
"She moves, in mysterious ways." - U2
*Backcasting, while interesting, has a definite hindsight is 20-20 feel about it.