Speed difference attributes vs elements

<problem
   models="long list"
   software_releases="long list"
>

<problem>
   <models>
      <model>...</model>    (many times)
   </models>
   <software_releases>
      <rel>...</rel>    (many times)
   </software_releases>
</problem>

Q1: Is there a performance penalty for either design?
Q2: Does the answer depend on the XSLT processor?

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