Well, I ended up enchanting my bow with a 100 points of drain health plus elemental damage/weakness and soul trap, and it's kinda absurdly powerful, so much so that my marksman levelling has slowed to a crawl. With this and master-level illusion spells I fear I have made the game a touch too easy (command - invis - shoot - invis - I never get touched), and may have to crank up the difficulty to compensate. Invisibility is amazing for Oblivion Gates though. Anyway, cheers all!
I'm glad you're having some success!
Yes, while still trying to level marksman, it is helpful to limit yourself to a bow that is just powerful enough to get the job done. My character held off on enchanting her top of the line bow until marksman was maxed. Prior to 100 marksman, she was interested in hitting lots of foes lots of times with her bow. After 100 however, she now makes a game of seeing how few arrows she can use to kill her foes.
The drain health x 1 sec is extremely powerful at lower levels. At mid to higher levels, when enemies have lots more hp, it will fade in effectiveness and you will likely want to replace it.