Best practice is to use /bin/path/to/servlet. 

Have you looked at lazybones templates? https://github.com/Adobe-Consulting-Services/lazybones-aem-templates

What version of AEM? Do you have the page history disabled as described in the URL below.  http://helpx.adobe.com/experience-manager/kb/slow-display-performance-welcome-page.html

You could try something like this. /jcr:root/content/dam//*[@jcr:primaryType='dam:AssetContent' and metadata/@dam:sha1='07614f5ec4a3bc5e3a822455fd52e1a0369429a0'] order by @jcr:scorePlease note that I have not tuned this query for performance, just something I cooked up. 

You can still search under a specific path. I am not sure I understand how for a particular property value affects what path you want to search under. 

I wouldn't do a fulltext search. the hash is stored in dam:sha1 property. I would just query that property.