For PvE, pretty much either composition is going to be fine in 5-man content.
I don't know how well the Enhance works, as I've not played that composition... and I haven't done much PvE (aside from Leveling and Playing the AH) in the last 2-3 years...

If there is not an enrage mechanic, 4x Blood with 1x Heals can do anything and it is rather trivial.
At least as far as pull size, number of mobs on you, etc.
If you need to control a vehicle or whatever, that's going to make class choice and class abilities irrelevant.
Last expansion, I'd think more people ran 4x Blood then 1x Blood and 3x Frost/Unholy, along with their healer... at least that was the impression, from those who are active on the forums.

I'd imagine 4x Shaman and a Tank is going to be fine as well.
You could spec one of the Shaman as Resto, and suddenly you have a Holy Trinity too.



For PvP...

I don't know that much about Enhance...
I do know that 5-box anything else, generally (almost every time) loses very quickly to boxed DK teams... but your metrics against another boxer is less important than how you do against non-boxed opposition that you encounter ~200x more often.

The Pally/4x DKs...

You have Obliterate, which hits really hard if the target has diseases on them (which you can apply with Outbreak).
You can spread your diseases with Blood Boil (and the Tier 1 Talent).

You have Howling Blast, which is 30 yard range.
It applies Frost Fever to everyone within 10 yards of the primary target.
With Chillblains, anyone with Frost Fever is snared.
Howling Blast doesn't hit a 90, nearly as hard as it hit 85s (in relation to their health)... but it still is AoE/Melee Cleave, which is huge to have and an immense issue if your composition doesn't have it.
I had my Howling Blast set to round-robin Chains of Ice (on one DK) and Howling Blast on the others... that way, even if one was dead, the kill target was basically constantly rooted.

Death Grip basically makes your team permanently immune to every Snare/Root effect in the game... as whether you move or not, the target comes to you.
With four Death Grips, and the glyph that refreshes the ability when you kill something that offers experience or honor, you basically have unlimited uses.

Icy Touch, with the glyph is purge; so both compositions have this.

The DKs have a lot of defensive cooldowns.
- Anti-Magic Shell makes you immune to anything that gives a debuff icon, for the 5 seconds it is up.
- Pillar of Frost makes you immune to knockback effects.
- Lichborne makes you immune (and breaks you out of) Fear/Charm/Sleep effects.
- Icebound Fortitude makes you immune to Stuns (and can break you out of them).
- Combined with a Trinket, that is two breaks of many effects which quickly brings into play Diminishing Returns.

At 90th, Desecrated Ground is an 8 second/2min CD immunity to Loss of Control effects too.
But you can also take the AoE stun, which with multiple DKs is applied much faster.

If you glyph your Pillar of Frost, it roots you but makes you immune to all 'Loss of Control Effects', for the duration.
You can macro it.... /cast PoF and /Cancelaura PoF... which is an extra trinket on a 1 min timer.
If you do, you are giving up the bonus STR from PoF.