OK, with CHDK 1.3 these are my results:
Free Memory Without Zebra Enabled:
1) just after startup, in playback mode: 1471264
2) after switching to rec: 1471264
3) after pressing and releasing half press once: 1471264
4) after shooting once: 1471264
5) after shooting twice: 1471264
Free Memory With Zebra Enabled:
1) just after startup, in playback mode: 1237576
2) after switching to rec: 1237576
3) after pressing and releasing half press once: 1237576
4) after shooting once: 1237576
5) after shooting twice: 1237576
NOTE: I noticed that my memory dropped as soon as there were images to display, because I repeated procedure again without zebra and got same results as with zebra, when I deleted photos, it went back to 1471264 bytes, which I believe is normal since it has to load thumbnails for display