first of all you have to decide Level of QA and what is the priority.
according to me i follow levels
first i will do positive testing which client or any end users are doing.
then after i move into different scenarios which can be done by tricky way or something different which is done by tricky user
then after i find the things which can be consider as non functional.
so i decide priority, based on that you will find reliable testing process and in minimum time you can achieve the testing for particular project...and it works for me..may be there are more seniors here and may be they have better idea. i hope my reply helpful to you.
Yes, you truly said, all such matters put the flow of work in more strengthen direction. An effective planning and knowledge about the release deadline prior to the commencement of testing phase in turns out an effective strategy. By maintaining RTM which ensures that every requirement is mapped through particular test cases.