I got curious, so I went in and did a little playing with the Console Commands. Keep in mind that "Finger of Death" is a Leveled spell:
http://www.uesp.net/wiki/Oblivion:Level ... e_Mountain
I checked with the level 1 spell, and the level 26 spell.
Using old Saves:
Character: Level 8, Destruction 17, Intelligence 50, Magica 100
Finger of Death: LV1 - Cast Cost 10
Character: Level 12, Destruction 32, Intelligence 68, Magica 136
Finger of Death: LV1 - Cast Cost 8, LV26 2755
Note: I made a Shock Damage Spell - 30pts, Casting Cost 47.
You can buy Spark, Shock Damage 10pts, Casting Cost 17.
I also made, Shock Damage 8 pts, Casing Cost 8.
Shock Damage 8 pts 10ft, Casting Cost 13.
Finger of Death LV1: 6 pts 5ft, Casting Cost 8.
Using Consol Commands:
Character: Level 12, Destruction 100, Intelligence 100, Magica 200
Finger of Death: LV1 - Cast Cost 2, LV26 710
From here it appears that if you increase your Destruction Skills, it will make the spell more doable.
Note: I made a Shock Damage Spell - 100pts 10ft for 2 Sec, Casting Cost 169
Also, Shock Damage Spell - 100pts 3 Sec, Casting Cost 169
Character: Level 12, Destruction 250, Intelligence 250, Magica 500
Finger of Death: LV1 - Cast Cost 2, LV26 Cast Cost 710
From here it appears that you do not get any more bonus, or rather lower casting costs for having your spell skills above 100. However, it would benifit you to Fortify your Intelligence, to get a higher Magica.
Note: I made a Shock Damage Spell - 100pts 10ft for 5 Sec, Casting Cost 424. 300 more Damage than Finger of Death.
If your Intelligence is 100, 200pts of Magica.
High Elf get 100pts of Magica.
Atronach Birthsighn gets 150 Magica.
You could get 450 Magica, you would still need potions a/o enchanted items to fortify 260 more magica points.
If you could Fortify your Intelligence to 250, you would get 500 Magica.
High Elf get 100pts of Magica.
Atronach Birthsighn gets 150 Magica.
You could get 750 Magica.
The drawback, is to get the 150 Magica from Atronach, you do not regenerate Magica, so it would be a one shot spell. You would have to have alot of Restore Magica Potions.