I find the gold wears off very quickly, even within a small project!!! So size is much more important and will depend on the linen you are using. You don't want too much friction going in and out of the fabric and you don't want holes in your work. Perhaps as small as possible taking into consideration the number of strands of floss you are using too.
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It doesn't matter as much as needle size. The golden tip makes the eye of the needle more visible (as in you know where it is on first glance), that's about it for me.