Updated Chinese Overlord image - Rise of the Reds mod for C&C: Generals Zero Hour

An armoured battalion on course to the east
Closing the end of it's march

This time we're here to finish a job
Started a decade ago
Driving the animals out of their holes
To bury them 6 feet below
Armoured tanks of mass destruction
Killers in the east
Rats who dares to stand before us
Feel our guns go live

Death in the shape of a panzer battalion
Insect of terror don't run face your fate like a man
Cannot outrun our panzer battalion

Thousands of tons of armour and guns
Making it's way through the sand
Our panzer battalion is back for revenge
Artillery sweeping the land

First strike is ours no mercy is shown
There's rivers of blood in our track
Breaking their lines of defence with our tanks
Infantry watching our back

Blow their sam sites clear for air strike
Ready for the storm
Minefields swept there's no surrender
Feel our napalm burn

Under this sun no shadows will fall
Piercing our eyes as we charge
An armoured battalion on course to the east
Has reached the end of it's march

The front hull is diffirent.

Frankly? While they're both the same type of tank, the Overlord probably still outsizes the X-66 by a lot.
And despite that, the C&C Wiki seems to say its guns are a 'mere' 125mm. Though, there is two of them, and they're almost as long as the tank itself, so muzzle velocities ought to be absurd, and I figure both tanks get depleted uranium APFSDS even if the game doesn't actively show* them for the Overlord*, and the Mammoth probably wouldn't use them much on Nod, having 120mm. I'm assuming Rheinmetall, but they too, could be something heftier.

*Not a lot of sense in using uranium for something else, I think.

Anyway, long story short and assuming a 'realistic' fight;
-If you placed them on opposing sides of an open field and let em at it in a 1v1, I'd put my money on a Mammoth without much actual reasoning.
-If you gave them infantry support and an actual wartime engagement somehow*, I'd still put money on GDI, but it would probably suck for them.

*Because what the **** kind of moron uses singular tanks and singular tanks alone?

And if you intend on actually making a game where GDI somehow goes up against Generals' China, the general differences between the factions would probably mean a Mammoth could duke it out with an Ovie and live, but there'd never be "An Ovie," in the first place.

Here's an extra tidbit free of charge; Mammoth's missiles are 60mm, and generally intended for Aircraft and personnel; Off the top of my head; He-Fragmentation warheads that turned out handy for murdering a bunch of infantrymen and were 'unofficially' pressed into the role. But anyway; Chinese infantry blobs probably wouldn't be overly appreciative of their existence.

there is actually a mod for generals that adds nod and gdi and then some.

Moddb.com

im not sure if it will ever finish. it seems to be dead but its one of those mods that gets an update every once in a while but i wouldnt hold my breath saddly

Overlord with the automated gatling could seriously screw the Mammy's optics though. Also the Overlord's ROF with the main guns seems a tad quicker than the Mammoth's.

Mammoth's can repair.

Depending on the calibre and muzzle velocity of the fixed gattling guns, they might have trouble landing on the optics without just bouncing harmlessly off the top of their armoured casings.

But if not, it still means that a 7.62, 12.7, 14.7 or 20mm round (Personally, assuming it's not the latter.) would have to hit a small target at a fairly high angle of attack by the time it reaches the target at anything but 'melee' range.

And then it would have to do the same thing to primary and secondary sights for both the gunner and commander. Handy for a distraction, I guess, but all-in-all, it should probably rely on using its main guns to throw the Mammoth's crew off-balance.

Self-repair would probably be a more important factor in-between separate engagements, and for recovery of knocked out tanks. Oooor a prolonged duel, I guess.

Greater or equal to 12.7 and the vibrations from the high RoF of the gatling's rounds simply landing in the vicinity of the optics would be enough to get some vibration going, let alone direct hits. The muzzle velocity I assume is pretty high due to the Overlords ability to engage low flying targets ranging from subsonic missiles to attack aircraft. Also means it's got excellent targeting/onboard radar.

Of course, the Mammoth is ultra modern in comparison to the Overlord, so it probably wins by default. Unless we're talking RA2 Apoc or RA Mammoth

That does, however, need at least enough accuracy from the gat to actually land all those bullets close enough to the spot.
Going by Chinese principle of quantity, that might be a bit of a problem for a single pair of guns.

Personally, I assume that at anything over a kilometre, the Chinese weapon would just land ricochets all over the exposed area of the Mammoth, failing to do much against the TD version.

On the other hand, the Overlord DOES have about 10-20 years on it, at least, but not very good ones on progress, if I remember, and it's still geared for mass-production.