ICS definitely improved battery life for me with the limited time I had the stock ICS update on my i777. I always do a complete backup with Titanium Back Up Pro, and wipe + upgrade. Granted you have to be rooted for Titanium, but it definitely helps. I went back to CM9, now on stable release, and couldn't be happier. Couldn't deal with all the bloatware.
Edit: And no, you don't have to remove your SD card for the update.
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