The behaviour can be observed when comparing JIRA 6.2.x with JIRA 5.2.11.

Steps to reproduce:

1. make sure JIRA 6.2.x and JIRA 5.2.11 has the exact same data
2. create same filter in both instances
3. add Filter Result gadget into the instances using the filter created in step 2.
4. access the dashboard and the JIRA 6.2.1 will be slower than JIRA 5.2.11
   the differences in speed is not obvious for small instance. In large instances and gadgets are used heavily, the response is obvious. In some cases, JIRA 6.2.1 with the same data as JIRA 5.2.11 it take 3 times longer to load the exact same dashboard.

The following result are sample log for Dashboard that has only 1 Filter result:

Based on Access log:

• JIRA 5.2.11

  127.0.0.1 1360x144x1 admin [04/Apr/2014:22:40:32 +0800] "GET /secure/Dashboard.jspa?selectPageId=10200 HTTP/1.1" 200 11969 135 "-" "Mozilla/5.0 (X11; Linux x86_64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/33.0.1750.152 Safari/537.36" "2zhbh9"
  

• JIRA 6.2.1

  127.0.0.1 1360x7388x1 admin [04/Apr/2014:22:40:51 +0800] "GET /jira621/secure/Dashboard.jspa?selectPageId=10200 HTTP/1.1" 200 12364 155 "-" "Mozilla/5.0 (X11; Linux x86_64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/33.0.1750.152 Safari/537.36" "12zmfnk"
  

Based on Profiling Log:

• JIRA 5.2.11

  2014-04-04 22:55:21,152 http-bio-7521-exec-11 DEBUG admin 1375x175x1 2s53d 127.0.0.1 /secure/Dashboard.jspa [atlassian.util.profiling.UtilTimerStack] [90ms] - /secure/Dashboard.jspa
    [0ms] - PermissionManager.hasPermission()
    [2ms] - Dashboard.execute()
    [0ms] - PermissionManager.hasPermission()
    [0ms] - PermissionManager.hasPermission()
    [0ms] - PermissionManager.hasPermission()
    [0ms] - PermissionManager.hasPermission()
    [0ms] - PermissionManager.hasPermission()
    [1ms] - PermissionManager.hasPermission()
    [0ms] - PermissionManager.hasPermission()
    [0ms] - PermissionManager.hasPermission()
    [0ms] - PermissionManager.hasPermission()
    [1ms] - PermissionManager.getProjectObjects()
    [0ms] - List.isEmpty()
    [0ms] - PermissionManager.hasPermission()
    [1ms] - PermissionManager.hasProjects()
    [0ms] - PermissionManager.hasProjects()
    [0ms] - PermissionManager.hasPermission()
    [0ms] - PermissionManager.hasProjects()
    [0ms] - PermissionManager.hasProjects()
    [0ms] - PermissionManager.hasPermission()
    [0ms] - PermissionManager.hasPermission()
    [5ms] - Rendering User Navigation Bar
    [8ms] - Rendering Top Navigation Bar
    

• JIRA 6.2.1:

   2014-04-04 22:53:49,950 http-bio-9621-exec-25 DEBUG admin 1373x7434x1 1ohpci3 127.0.0.1 /secure/Dashboard.jspa [atlassian.util.profiling.UtilTimerStack] [147ms] - /jira621/secure/Dashboard.jspa
    [0ms] - PermissionManager.hasPermission()
    [49ms] - Dashboard.execute()
    [0ms] - PermissionManager.hasPermission()
    [0ms] - PermissionManager.hasPermission()
    [0ms] - PermissionManager.hasPermission()
    [0ms] - PermissionManager.hasPermission()
    [0ms] - PermissionManager.hasPermission()
    [0ms] - PermissionManager.hasPermission()
    [0ms] - PermissionManager.hasPermission()
    [0ms] - PermissionManager.hasPermission()
    [0ms] - PermissionManager.hasPermission()
    [0ms] - PermissionManager.hasPermission()
    [0ms] - PermissionManager.getProjectObjects()
    [0ms] - Collection.isEmpty()
    [0ms] - PermissionManager.hasPermission()
    [0ms] - PermissionManager.hasPermission()
    [0ms] - PermissionManager.hasPermission()