Ground Rules

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 StormlanceLeane Stormlance20
Dragonbane FlowerCalindril40
Dragonbane FlowerBalion Tearwing40
Drum of VictoryZelim80
Dragon Leader's EggSir Charles Quixote[80]
Dragon Leader's EggDeftclaw Redreaver[80]
Ebonest {Champion}Sir Charles Quixote100
Sword of Whistlebone {Great Wyrm}Deftclaw Redreaver100
Slay all DragonsAvalon80
Kill all Dragon HuntersJerin Flame-eye80
Regna 62
Stanley's TreasureOne-Eye (if main character talks)62
Ironsand Desert 254
Fire ResistancePole6x4+30 = 54
Pure EnduranceTalion20
Ashes to TombOverduneSnapfinger80
Ancient Troll Home {War Troll}Volog Sandwind100
Ravage Roaming 200
Pure AccuracyGalvinus20
Drain LairThanys80
Axe of Balthazar {Minotaur Lord}Tessalar100
Alvar 280
Pure LuckRihansi20
Eliminate OgresKeldon40
Witness to Lake of FireBastian Loudrin40
3 CheesesAsael Fromago80
AllianceBastian Loudrin0
Cauri {Patriarch}Relburn Jeebes100
Murmurwoods [200] + 120
Pure PersonalityCastigeir20
Skeleton TransformerOskar Tyre[200]
Prophecies of the Sun {Priest of the Sun}Stephen100
Ravenshore 2738
Rescue IrabelleArion Hunter20
Dire WolvesMaddigan30
Letter to Arion HunterElgar Fellmoon48
See Bastian LoudrinElgar Fellmoon60
False Report to StanleyArion Hunter80
Arcomage ChampionshipBlueswan200
Sink Regnan fleetCouncil400
See XanthorCouncil0
Heart of AirXanthor0
Heart of EarthXanthor400
Heart of FireXanthor0
Heart of WaterXanthor400
Elemental HeartsXanthor1000
Source of CataclysmXanthor0
Shadowspire [50] + 458
Pure IntellectKelvin20
Bone of DoomTantilion30
Nightshade BrazierSandro[50]
CureBlazen Stormlance60
Iseldir's Puzzle BoxBenefice60
Vial of Grave DirtHallien88
Sarcophagus / Remains of Korbu {Nosferatu}Lathaen100
Lost Book of Kehl {Lich}Vetrinus Taleshire100
Dagger Wound Island 118
Find Dadeross-0
Crystal to TalimereBrekish Onefang6
Pure SpeedThistle4
Find IsthricRohtnax3
Yellow FeaverAislen6x1+6 = 12
Prophecy of the SnakeTisk3
Idol of the SnakeHiss30
Letter to Elgar FellmoonDadeross30
Plane between Planes 1600
Lord of AirEscaton400
Lord of EarthEscaton400
Lord of FireEscaton400
Lord of WaterEscaton400
Free Elemental LordsEscaton0
Total of all quests [150+] 6500
Bounty Hunt 160
Novice Bounty HunterGuild of Bounty Hunters160
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.