It's fairly unlikely that either solution would work out. I would think that the best idea would be to find the performance problem and fix it.
MySQL is very fast, even with very large databases, if you construct your queries properly.
Here are some suggestions:
1) Make sure that as much database access as possible is done via primary keys. When you have to retreive data by something other than a primary key, make sure that you have a proper index, and that the index is being used (Google MySQL "Explain Plan" for more info).
2) Don't use functions in your WHERE clauses
See "Explain Plan" for this too.
3) Make sure that you don't do any unneccessary database access. Consider some means of caching wherever possible.