I was hoping someone else with more experience would respond to your post…
It is always true that with Monte Carlo sampling, your initial sampling must be high enough that the highlights you are attempting to capture cover multiple pixels. You can probably improve your result simply by increasing -x and -y beyond 600 in this case. How far beyond you need to go, I am not sure, but you can try doubling it.
Another factor is that rpict looks specifically for small-area light sources in its calculation, whereas rtrace does not. This can have an effect on the size and accuracy of the solar orb integration, but will not help on the reflections. In fact, unless you set -ps 1 for rpict, you may miss important reflections that rtrace will catch, similar to the issue with the shadows from venetian blinds in your previous post.
Cheers,
-Greg