What are the possible benchmarks that can give an idea about search performance in SharePoint Server 2013 ?
You should download and test the SharePoint SRx Search Health Reports. These reports provide tons of deep metrics on the search service application. Pay attention to Crawler Health and Index Reports with:
$xSSA | Get-SRxIndexReports -DiskReport
So with Search in my opinion the Crawl Rate and Query Time are most important, as they affect the experience. The Test for 2010 can give you indication what to expect. https://technet.microsoft.com/en-us/library/ff599526(v=office.14).aspx . The scaling article will give you guidance which resources are most important. https://technet.microsoft.com/en-us/library/dn727118.aspx. Search is IOPS hungry and the faster disk you can give it the better. I have some fantastic experience with ExtremeIO (SSD storage). The values for crawl rate and queries you can find in the search report in search service administration.