Notes

Metamoran Fusion Multiplier is (a+b)^10=?
Potara Fusion Multiplier is (a+b)^10X~[]=? [Rival Boost=1.3X/Blood Boost 3X/Identical Boost 5X]

Lets get the multipliers for each SSJ from base. (Plus Kaioken)
Kk= Users Base^* (* is equal to multiplier, I.E. ^20)
SSJ= 50X
SSJ2= 100X
SSJ3= 400X
SSJ4= 200,000X (This is an extreme Highball. It was originally 4,000X, but I did some magic and multiplied both the 10x Oozaru and the default 50X SSJ, then multiplied it to SSJ3's Multiplier)
SSJG= 200,000X (Was originally 500,000X But I Lowballed it)
SSJB= 10,000,000X (Was 25,000,000X But I also Lowballed it) (Multiplied SSJG with SSJ)
SSJR= 10,000,010X
SSJBE= 10,000,020X

Now let's get the power levels from both Broly Movie Gogeta, and GT Gogeta.
Because neither of them have traceable power levels, let's just get a baseline, a lower number for simplicities sake; and both Gogeta's are at that level in base.

Let's just say they have a hypothetical level of 50. (Goku has a power level of 2 and Vegeta has a power level of 3.)
In their strongest forms, Gogeta Blue has a power level of 500,000,000. About the same as Semi-Perfect Cell.
SSJ4 Gogeta would have a power level of 10,000,000. Meaning he would stomp Third form Frieza.

With all of this math done, and generous highballing in favor of SSJ4 and Low Balling SSJB, it is with great sadness that I finally give the truthful answer.
SSJB would eat SSJ4 Alive. No matter the day. Now this is only factoring in End of Super Broly and After the Omega Shenron fight. So No Xenoverse, No Fighterz, No Dragon Ball Heroes, and No Headcanon. (Minus giving them the Hypothetical power level of 50.)

Now let's say that base GT Gogeta has a power level of 200, and base Broly Gogeta has a power level of 50.
200*200,000= 40,000,000. SSJ4 Gogeta has a power level max of 40,000,000
50*10,000,000= 500,000,000. Still, with a slight handicap, SSJ4 loses.

Let's Highball GT Gogeta even more, putting him at Raditz Level, and keeping Broly Gogeta at a power level of 50.
1,200*200,000= 240,000,000. SSJ4 Gogeta has a max of 240,000,000.
Gogeta Blue would still dominate SSJ4 Gogeta. Even after all these Highballs.

Once again, we will be highballing GT Gogeta. This time he's at Nappa level.
4,000*200,000= 800,000,000.
Now we see Gogeta SSJ4 finally dominating Gogeta Blue. But it took SSJ4 Gogeta to get to Nappa level to dominate Gogeta Blue with early Dragon Ball power levels.

~Extra Time~
Zamasu Saga Vegito vs Shadow Dragon Saga Gogeta.

Let's say Zamasu Saga Vegito has a power level of 35 while Shadow Dragon Saga Gogeta has a power level of 2,000
35*10,000,000^1.3= 455,000,000. Vegito Blue would be at 455 million.
2,000*200,000= 400,000,000. 400 Million. That's nothing to scoff at. If Shadow Dragon Saga Gogeta SSJ4 was to fight Zamasu Saga Vegito Blue, Vegito would win in an extremely close match.

This took me 2 and a half hours of math to do so please be mindful of my mental state. I did my best to highball SSJ4 and Lowball SSJB, but even if they were even in base, they wouldn't be even in their transformations.