You give that +7 speed way too much credit. You will not outspeed anything because you are still a human mage.
Stick with BW light, if you manage to get +8 set (yes, they exist if you ever get there) you will get some good bonuses, including your beloved speed boost (+4).
If you really don't wanna heal your party, you can still kite/root frontliners but purification song will make it mostly a waste of time and MP.
That's how the game is right now.
For tankiness +4 con +8 wit is acceptable. If you go less wit, your healing capabilities will take a massive hit (casting spd/crits of heal).
Which is also why I would pick BW over Doom (ALSO stuns are more common than root/sleep).
Bow/Melee setups outside are not even worth discussing, go for 1-handed magic weapon and shield.
Cheers.