Mournfangs GW or IF?

I used them to add variety to my Ironguts. They are really cool GWs.

thats my plan. use the arms for them on normal ogres and some normal ogre hands to add the IF and hand weapons too

I'm rather partial to saving the Mournfang GW's for character conversions. Nothing says Tyrant like an extra-big greatsword!

I have 2 units of 4 with Iron Fists, if I add a third unit, they'll have great weapons, but probably never get played, and if they do get played, I'm going to call them "parrying staves" instead of great weapons and count them as Iron Fists.

TH boost in strength seems tempting. But the truth is, the Mournfang do most of the damage..with impact hits, and attacks at str 5.  Also, the dragonhide banner mitigates any damage loss by switching from Great Weapons to Ironfists

True, the DHB does mitigate the strength loss and I can't really argue much against the IF (as I do think it is the better choice).  That said, the GW does have two positives.  First, only one unit can carry the DHB and only one MC unit can carry a magic banner at all.  In this case, if you have 2 MC units and one has the DHB, then the other could get a little boost in power from the GW.  This also presents a difficult target priority (as 2 MC usually do) with the enemy choosing between a 3+ armor but cheaper unit with no magic banner, and a 2+ armor with the DHB on a more expensive unit.

The second thing the GW add is a more powerful punch.  Yes, the Rhinox does most of the work on your typical MC unit, but with a GW the ogre won't be as far behind.  Both units are essentially going last anyway with I2 so the GW strikes last special rule isn't as detrimental.  Also, the unit is equiped to hunt bigger things.  But the real difference is that the GW unit isn't planning on sticking around for another round of combat but rather scoring enough kills to break the unit in the first round.

That said, I still agree the IF is better ha ha ha; but not so terribly better that I would mind having a second unit with GW every now and then to change things up.

Completely agree with this... While the mandatory unit is IF + DHB, a second one can possibly be GW for more versality (high AS enemy, high T monsters and stuff...)

Given that I build up my two MC from the box with IF, how many extra arms i get exactly and how equipped?