If wife and I are both GM.
Would split PNR provide a better upgrade chance or it doesn't really matter since we are the same status?

This is a good question. If one of you were Silver or Plat, I would definitely split.

More than 90% of the time, either NEITHER of you will be upgraded (because Diamonds and Plats got them all), or BOTH of you get upgraded (because there are two or more seats left for Golds).

The question is what happens if there is one seat open and the upgrade queue says the two of you are next. I think the queue jumps to to the next "party of one". Unlikely that any couple has ever been called up by the gate agent and told, "I have one upgrade left. Tell me which one of you gets it."

The default for Delta is NOT to split up parties of two or more for upgrades.
I wish Delta had an "Allow Separate Seating for Upgrades" check box in our personal preferences on Delta.com

Not all Golds are equal. There are various other factors that come into play.

So, by splitting the reservation you may be increasing the odds for one of you.

The last time in travelled with the Mrs on a joint PNR (DM & GM) I was paged by the GA on both legs outbound and asked if I wanted to be upgraded even though my wife would not be. (The answer is obviously yes - and it's not me that sits up there).

On the return I proactively told the GAs to process 1 upgrade. We were on award tix and made all 4 upgrades on that trip