Removing php extensions in IIS with Ionic's Isapi Rewrite Filter

I couldn't get this to work as well as I wanted, or with the rules as clean as I wanted. I know there must be a better way, so I encourage comments, or contact me if you know of a better way. I did achieve all of my important requirements, though, for my specific application:

• For a resource or downloadable content (like jpg, css, zip, etc), leave the extension.
• If requesting a directory (URL ending with /), try first for index.php, then index.html, then index.htm.
• If requesting a non-directory location that doesn't exist (like /whatever), look for whatever.php, whatever.html, and whatever.htm in that order, and use the first one found. I do rely on IIS's behavior that if the user goes to /somedir and somedir is a directory, it redirects them to /somedir/, then my rules will look for index properly.

I allowed direct links with .php on the end to work, and I didn't redirect those to the "php-free" URL, but this is something I think is easily possible. Here is my configuration:

RewriteEngine ON
#uncomment this to enable the iirf status page (see documentation)
#StatusInquiry ON /iirfStatus RemoteOk

IterationLimit 5

# don't rewrite any request that ends with one of these extensions,
# even if they don't exist.
RewriteRule (.+\.)(jpg|png|jpeg|gif|ttf|sql|txt|zip|css)$   -   [L]

# If there is an exact match, then don't do any rewriting
RewriteCond %{REQUEST_FILENAME} -f
RewriteRule ^.*$ - [L]

#If this is a URL ending with a /, try index.php, then index.html
#(I don't know how to get it to search as if we had done /index):
RewriteCond %{REQUEST_FILENAME}index.php -f
RewriteRule ^(.*)/$  $1/index.php [L]
RewriteCond %{REQUEST_FILENAME}index.html -f
RewriteRule ^(.*)/$  $1/index.html [L]
RewriteCond %{REQUEST_FILENAME}index.htm -f
RewriteRule ^(.*)/$  $1/index.htm [L]

# Try to see if this is a PHP page:
RewriteCond %{REQUEST_FILENAME}.php -f
RewriteRule ^/(.*)$  /$1.php [L]

# Try to see if this is an HTML page:
RewriteCond %{REQUEST_FILENAME}.html -f
RewriteRule ^/(.*)$  /$1.html [L]
RewriteCond %{REQUEST_FILENAME}.htm -f
RewriteRule ^/(.*)$  /$1.htm [L]