1) You're optimizing for a problem you don't even know you have.
2) Extracting bytes from a register may well slow things down significantly (where significantly = no real increase).
3) If you're so low on memory you can't spare 128 bits (even on cell phones, 8,589,934,592 bits is easy) for animations, you've probably got other, more important problems.
4) Rotation might be slightly choppy.
So, in short:
1) Make sure you know what the problem actually is before you try to fix it.
2) At least static-test your solution concepts.
3) Don't optimize where you don't need to.
4) Something to check.