Concerning tithing and Malachi 3...
I believe that 2 Peter 1:3-4, Hebrews 11:33, 2 Corinthians 1:20, and Romans 4:20-22 speak of the fact that there are promises in the OT that we can take a hold of by faith.
So as a general guideline, I count tithing a tenth as being a condition for a promise according to Malachi 3.
While if we give more or less, Luke 6:38 and 2 Corinthians 9:6 (in its immediate context) would tell us that we will receive back more or less respectively (whether the blessing be financial or spiritual...see Ephesians 1:3).
But if you want a blessing that you will not be able to receive, it is so great, then bring the whole tithe (tenth) into the storehouse; for that is the promise of holy scripture.
There is more on this subject in the other current thread on this subject.
Link:
Is it ok to Give = $$$$$$$