As discussed in this answer, Krishna is a rare philosopher, who related "I / Me" with the ultimate supremacy during the discourse of Gita. That implies that the "I / Me" resides in every being & non-being & is also beyond them.
When I read below verses again & again, it makes me feel like the "I / Me" are beyond the "Brahman" as well, and are not same.
BG 8.16 - All planes along with BrahM-plane are repetitive, O Arjuna. But reaching "Me", O son of Kunti, the rebirth doesn't happen.
BG 8.17 - Knowing that thousand eras constitute a day of Brahman, [and] thousand eras complete a night, are the people who know day, [and] night.
BG 13.13 - I shall speak of that which is knowable (should be known). Knowing which, one attains immortality. The supreme Brahman dwelling under Me, is beginningless. "That" is said to be neither existent nor non-existent."
BG 13.14 - That (Knowable), which has hands and feet everywhere, which has eyes, heads and mouths everywhere, which has ears everywhere, exists in creatures by pervading them all.
BG 14.27 - For 'I' am the Abode of Brahman-the indestructible and immutable, the eternal, the Dharma and absolute Bliss.
- BG 8.16, 8.17 suggests that, if one reaches BrahM (or Brahman), then still that one has to repeat. Because, even Brahman also has day & night, which is ~24 million years, as discussed in this answer. However, "I / Me" is timeless, hence no return.
- BG 13.13 GambhirAnanda's also translates: Supreme Brahman dwelling under 'Me'.
- BG 13.14 Read "clarification" section.
- BG 14.27 also suggests as "Brahman" is in 'My' abode.
Often in this site, we all interpret Brahman as supreme. But at least the translations of above verses are differing in nature. My guess is that, the "I / Me" represents, what we call Nirguna Brahman.
Is there any other scriptural or philosophical reference, which shows relation between "I / Me" & Brahman?
Clarification: There is always a confusion between, Brahman (supreme one) and BrahmA (4 headed deity). Now, in Gita there is no mention of such formful deity. I am not sure, even in MahAbhArata, such mention will be there. This seems more of a pictorial representation by devotees, which is coming since centuries.
My theory: According to BG 13.14 verse, Brahman is having "heads everywhere". Not only heads, but eyes, hands, feet everything, everywhere. In old times, people wanted to represent this Brahman, hence they painted with "4 heads & several hands". May be with time & interpolations, this Brahman became BrahmA and further became an [inferior] part of trinity.
This is similar to how pictorial representation of Vishnu is done, by 'pervading throughout the universe':
BG 9.4 - This whole world is pervaded by Me in My unmanifest form. All beings exist in Me, but I am not contained in them!
Hence, it's safe to assume: Brahman = BrahmA = BrahM, in context of this question.