I think I read they do 1250 per Krak, where as a Meltabomb is 4000.

Pretty sure Karks got nerfed vs vehicles. I know Orks got overlooked for a while so I could 2 stikky and 3 rokkits to kill a vehicle. 1 Supa and 3 rokkits did the same. Now I need a 4th rokkit with 2 stikkys

Put four on the back of a tank. It has the same effect as 2 meltas.

Yep, hadn't noticed that! Good they changed it.

4 * 1250 = 5000.

4000 * 2 = 8000

8000 > 5000

Ork better at math than puny Eldar.

If a vehicle only has 5000 HP than 4*1250 = 2*4000 in practice.

I'm positive it takes more than 2 meltabombs to kill a Rhino. Do they do bonus damage if placed on the back, though? Cuz I wasn't doing that.

They do reduced damage if not placed on the back, @Slayer88. 2 meltas on the back = dead vehicle.

Testing it on uat now. Definitely less than half damage on the side.

6 Krak to take out a rhino on the rear.
8 Krak on the side.
14 Krak on the front.

2 Melta on the back.
3 Melta on the side.
4 Melta on the front.

So there you go.

Against a Grav Tank, sure, they have less health (4800 for Serpent?)

Against Rhino and Trukk, I'd take the Melta Bombs.

Keep in mind that the Meltabomb isn't just more useful against vehicles, it's also more expensive.

Destroying tanks is not my primary duty, I'm not using a lascannon or a meltagun. So a huge factor outside of the effectiveness is that 200LP cost. 70LP for a weapon that does even 30% of the damage to a vehicle but that is also useful in other situations is something worth noting.