Here, I had another go at this. Please cross-check, if you wish.
Ethernet frame (not jumbo):
7 bytes: Preamble (LSB-first = 0b10101010 = decimal 85)
1 byte: Start of Frame Delimiter (0b10101011 = decimal 213)
6 bytes: Destination MAC
6 bytes: Source MAC
[4 bytes optional]: VLAN Tagging
2 bytes: Length (max 1500) or EtherType (e.g. 0x806 = ARP)
N bytes: Payload (46..1500)
4 bytes: CRC
12 bytes: Interpacket gap
Smallest total overhead (without VLAN) is 38 bytes, for utilisation of 97.53%, or 975292587 bytes/second of IP frames.
Put another way, GbE can carry 81274.382 1500 byte IP packets per second.
IP Frame format:
1 byte: Version (= 4 for IPv4), IHL (header length, number of 32-bit words, minimum 5)
1 byte: TOS, which is now DSCP (6 bits), Explicit Congestion Notification (2 bits)
2 bytes: Total length (minimum 20, including the header. 576 bytes guaranteed fragment reassembly)
2 bytes: Identification (used for fragment reassembly)
2 bytes: flags (3 bits: Reserved, Don’t Fragment, More Fragments) and fragment offset (13 bits, units of 8 bytes)
1 byte: TTL; decrements by one on each hop, packet discarded when zero
1 byte: Protocol (1=ICMP, 2=IGMP, 6=TCP, 17=UDP, etc)
2 bytes: Header checksum
4 bytes: Source IP
4 bytes: Destination IP
0-40 bytes: Options
0..65515 bytes: Payload
Smallest total overhead is 20 bytes (max payload in 1500 byte Ethernet is 1480 bytes)
UDP Frame header format:
2 bytes: source port
2 bytes: destination port
2 bytes: length (set to zero in a jumbo gram >65535 bytes)
2 bytes: checksum of header&data (optional in IPv4, set to zero)
Total overhead is 8 bytes. Max UDP payload in Ethernet is 1472 bytes.
Payload bits/second over GbE is therefore 957087126, which is more than 76.8*12 bits = 921Mbps.
It’s theoretically possible.
Clifford Heath