[0.96] A whole lotta awesome

Ratio of Oblivion Guardians: 54 hp per exp, 5% damage reduction.

Let's assume that, after you get your precious 250%, you get the harsh penalty for sharing with 5 other people (though you get their exp, as well as party bonus, as well as HS), and brings it to 150k exp or so. Maybe 160k or 170k.

9m for 150k: 60 hp per exp, 30% damage reduction.

Yeah, huge difference. The only way this is topping Temple of Time is if the 250% boost can turn that 50k into 200k through extra bonuses.

Harsh penalty? Indeed?
Let's do a bit of math.

Party exp formula goes something like this:
Exp = monster_exp * ( (0.6 * damage_done / total_monster_hp) + (0.4 * your_level / sum_of_party_levels))
If HS is present, multiply by 1.5. However, the total is capped by 1.1 times the monster's exp.
Party_bonus = 0.05 * party_size * Exp

So, let's assume you are killing mobs that give 10k exp each, and you're in a party of 6 (including HSer), all about the same level, and you're the only one killing.
You get 10k * ((0.6) + (0.4 / 6)) * 1.5 = 10k... exactly the same as you'd have gotten all alone. But wait, party bonus! Normal party bonus, nothing to do with LHC, is 0.05 * 6 * 10k = 3k.
So, by having 5 leeches including HS hanging on ropes with you at any training map at all, you can get 30% more exp than you can when you solo.

You think that's all due to HS? Think again. If it were just you and the HS'er, your Exp would be 11k (since it's capped by 1.1x the monster's exp), and party bonus would be 1.1k (10%, since there are only 2 of you), so together that would be 12.1k. Still less than the 13k per kill you get with a full party of leeches.

And, as I said, that's in normal training maps.

At LHC, party bonus is ten times that. So that 10k kill gets a 30k bonus, for a total of 40k. 4 times the exp you'd get if you just went solo.

Now, if the other party members actually do some killing as well, and you get a slice of that (1k Exp and 3k party bonus per kill, I leave the math to you), that adds up to some really nice pocket change. Assuming all 4 of them (minus the bishop) are killing about as fast as you are, that's 16k more exp you get in the time you kill one mob. So, total of 56k exp instead of 10k you'd get soloing.

Harsh penalty, indeed.

(Final note: mobs in LHC give considerably more than 10k, was just using that nice round number for demonstration purposes).