I sat down one day a while back and did some calculations on what some actual mana savings would be for the various effects under different casting conditions. There is also a spreadsheet link for anyone who likes details.
I used it to help decide things like the relative value of FT3 versus MP4. Follow the link below if you're interested. Hope it helps.
Your Mana and You
Diminimus
63rd Illusionist
Morell-Thule
Council of Zarchon