I have written a hack of a class that allows you to do some quick testing of your site.
The class is part of our templateoverview module - which helps developers understand, test, review and simplify Page Types. HOWEVER, the tasks can be used on its own.
You can find the class here:https://github.com/sunnysideup/silverstripe-templateoverview/blob/master/code/tasks/CheckAllTemplates.php
It works with SS3.1, but other versions (albeit less developed) are available too.
What it offers:
(1) checks all basic screens for 200 response
(2) checks response time for all basic screens
Basic screens are:
* all page templates (page types)
* all basic CMS views (e.g. add new page, edit existing page, basic model admin views).
* you can also add your own URLs
To try it out, just copy the class into your mysite/code/tasks folder. Run a ?flush=all and browse to:http://www.your.site/dev/tasks/CheckAllTemplates/
Happy testing (feedback appreciated - of course).
PS this is what the test looks like: