Score in Might & Magic VIII is measured as the main character's experience / Time, where time is the number of days completed. Fame is 4x the main character's experience / 1000. With respect to score, a new day starts at 9:00 am. Experience is gained by killing as well as by completing quests. Since the outcome can be influenced by other factors than merely good gameplay, a few groundrules are necessary to make scores compatible. The following "cheats" are out.

[1] Respawning (Pirates, Snakemen, Skeletons)
[2] Reanimating (Dark spell)
[3] Repeated kills (by paralysis, or if there's no room for the body to drop down)
[4] The learning skill (a bug, it should affect experience but not score)

If these ground rules are not followed, scores will be uncomparable.

In addition, I took care to have a full party at each promotion, in order not not exploit the promotion bug(?) (5 x the amount shared by the party as is, instead of 1 x the amount for each member as with all the other quests).

Let's see, how high scores can become if the ground rules are followed.
The following table shows how much fame is involved with the quests in Might & Magic VIII.

Quest	From	Fame
Garrote Gorge		620
Blazen Stormlance	Leane Stormlance	20
Dragonbane Flower	Calindril	40
Dragonbane Flower	Balion Tearwing	40
Drum of Victory	Zelim	80
Dragon Leader's Egg	Sir Charles Quixote	[80]
Dragon Leader's Egg	Deftclaw Redreaver	[80]
Ebonest {Champion}	Sir Charles Quixote	100
Sword of Whistlebone {Great Wyrm}	Deftclaw Redreaver	100
Slay all Dragons	Avalon	80
Kill all Dragon Hunters	Jerin Flame-eye	80
Regna		62
Stanley's Treasure	One-Eye (if main character talks)	62
Ironsand Desert		254
Fire Resistance	Pole	6x4+30 = 54
Pure Endurance	Talion	20
Ashes to Tomb	OverduneSnapfinger	80
Ancient Troll Home {War Troll}	Volog Sandwind	100
Ravage Roaming		200
Pure Accuracy	Galvinus	20
Drain Lair	Thanys	80
Axe of Balthazar {Minotaur Lord}	Tessalar	100
Alvar		280
Pure Luck	Rihansi	20
Eliminate Ogres	Keldon	40
Witness to Lake of Fire	Bastian Loudrin	40
3 Cheeses	Asael Fromago	80
Alliance	Bastian Loudrin	0
Cauri {Patriarch}	Relburn Jeebes	100
Murmurwoods		[200] + 120
Pure Personality	Castigeir	20
Skeleton Transformer	Oskar Tyre	[200]
Prophecies of the Sun {Priest of the Sun}	Stephen	100
Ravenshore		2738
Rescue Irabelle	Arion Hunter	20
Dire Wolves	Maddigan	30
Letter to Arion Hunter	Elgar Fellmoon	48
See Bastian Loudrin	Elgar Fellmoon	60
False Report to Stanley	Arion Hunter	80
Eclipse	Lathius	100
Arcomage Championship	Blueswan	200
Sink Regnan fleet	Council	400
See Xanthor	Council	0
Heart of Air	Xanthor	0
Heart of Earth	Xanthor	400
Heart of Fire	Xanthor	0
Heart of Water	Xanthor	400
Elemental Hearts	Xanthor	1000
Source of Cataclysm	Xanthor	0
Shadowspire		[50] + 458
Pure Intellect	Kelvin	20
Bone of Doom	Tantilion	30
Nightshade Brazier	Sandro	[50]
Cure	Blazen Stormlance	60
Iseldir's Puzzle Box	Benefice	60
Vial of Grave Dirt	Hallien	88
Sarcophagus / Remains of Korbu {Nosferatu}	Lathaen	100
Lost Book of Kehl {Lich}	Vetrinus Taleshire	100
Dagger Wound Island		118
Find Dadeross	-	0
Crystal to Talimere	Brekish Onefang	6
Pure Speed	Thistle	4
Find Isthric	Rohtnax	3
Yellow Feaver	Aislen	6x1+6 = 12
Prophecy of the Snake	Tisk	3
Idol of the Snake	Hiss	30
Letter to Elgar Fellmoon	Dadeross	30
Antidote	Languid	30
Plane between Planes		1600
Lord of Air	Escaton	400
Lord of Earth	Escaton	400
Lord of Fire	Escaton	400
Lord of Water	Escaton	400
Free Elemental Lords	Escaton	0
Total of all quests		[150+] 6500
Bounty Hunt		160
Novice Bounty Hunter	Guild of Bounty Hunters	160
Promotion of main character		100
Total of all awards		[150+] 6760

For some obscure reason, allying with the Clerics of the Sun is valued much higher than allying with the Necromancers.
There are more Bounty Hunter awards, but only the title of Novice is attainable in a fast game. The total amount of fame from awards is about the same as in Might & Magic VII.

Additional fame comes from killing foes, including any Arena fights, and even from killing friends. It is important to notice that while awards give a set amount of fame to each character, experience from a kill is divided among all conscious party members. Hence, members of a small party gain more fame from the same kill than members of a large party. Of course it is harder to make that kill in the first place when the party is small.

There is sufficient prey in the game to gain almost 5000 fame from killing for a full party. This too is comparable to Might & Magic VII.
The fastest time, 24 days as in Callisto's run, does not offer enough slack to attain a maximum score. For that, one extra day of killing should be sufficient. A maximum score would be close to 120,000.
Higher scores are, however, obtainable with a smaller party, even though this slows down the progress. A party of three is probably optimal for individual kills, but for mass killing by Armageddon a party of two (or even one, if the main character is a Lich or has a bunch of scrolls) suffices. With some effort, scores of about 300,000 are conceivable - still without respawns and the learning skill.

Note that with 17 horseshoes, 1 game, 2 contests, 3 tests, 3 challenges and the three buoys the main character has a maximum of 110 skill points to distribute over various skills, not counting diamonds. This allows a Lich to become M7 at Dark Magic (for Armageddon) and G12 at Learning, for a bonus of 69%. Therefore, impure scores could approach 500,000.