htaccess rules for a WPMU 3.2.1 site with sub-domains

I am finding that performance is slow on my site when people upload files. Looking at the stacktrace, it's pointing to /wp-includes/ms-files.php as the problem.

I wonder if this relates to our .htaccess rules, which are left over from when we ran WPMU 2.x

A more recent test install includes this:
# uploaded files
RewriteRule ^files/(.+) wp-includes/ms-files.php?file=$1 [L]

but our production install includes this:
#uploaded files
RewriteRule ^(.*/)?files/$ index.php [L]
RewriteCond %{REQUEST_URI} !.*wp-content/plugins.*
RewriteRule ^(.*/)?files/(.*) wp-includes/ms-files.php?file=$2 [L]

Can you tell me what the current, preferred htaccess rules are for a multisite network, using HTTPS for /wp-admin/ and sub-domains for blogs. Thank you.