[Fun Fact, or, rather, Fun Speculation: If we use the Super Exciting Guide multipliers for Super Saiyajin 1, 2, and 3, as well as the Dragon Ball GT Perfect Files’ speculation that Vegeta’s final form (when possessed by Baby) before Super/Golden Oozaru is Super Saiyajin 3, along with a few reasonable assumptions (which, unfortunately, is necessary), we can infer what the multipliers for Super Oozaru and Super Saiyajin 4 are.
SSJ3 Gokuu was outmatched by SSJ1 Vegeta-Baby; since SSJ3 = 400x Saiyajin and SSJ1 = 50x base Saiyajin, it is reasonable to assume that Vegeta-Baby, when in the same form as Gokuu, is roughly 10 times stronger than Gokuu, making SSJ1 Vegeta-Baby approximately 500x base Gokuu. The presumed SSJ3 Vegeta-Baby was concerned by Super Oozaru Gokuu, implying that Gokuu was a threat in that form, which would make Gokuu at least equal to or in slight excess of SSJ3 Vegeta-Baby. This would require an approximate multiplier of 5000x, as SSJ3 Vegeta-Baby is around 4000x base Gokuu.
However, as Vegeta-Baby also goes Super Oozaru, we must also apply the 5000x multiplier to him. This means that Super Oozaru Vegeta-Baby is approximately 10x Super Oozaru Gokuu. In order to match this, Gokuu must get 10x stronger on top of Super Oozaru; this means that SSJ4 must have a multiplier of at least 50000x. As the GT Perfect Files state SSJ4 Gokuu and Super Oozaru Vegeta-Baby to be approximately equals, 50000x works very well.
Incidentally, 50000x is also the multiplier I use for Super Saiyajin Blue, as it is what happens when a Saiyajin who has absorbed Super Saiyajin Red/God into his body and mastered it goes Super Saiyajin.]
