Im running php scipts with many MySQL queries. Since the server loads are getting high, I thought the caching features of MySQL 4 will bring relief.

Now there are several things I'd like to know before taking the adventure:

1) Is the caching feature effective on all Table kinds? All my tables are of typ MyISAM. Do I have to convert them? Should I convert them for better perfomance?

2) When switching to 4, do I have to update the old (3.23) Version, or can I have both installed on one maschine to easily switch back, if I reget it for some reasons?

3) I am thinking of using the Zend Performance Suite (ZPS). This too has some MySQL caching as far as i understood. Will the caching through the ZPS be obsoulete when using MySQL 4? After ZPS ist very expensive and MySQL 4 not!

4) Is there anything else i have to think of when upgrading>

Thank you