The driver can sustain the full 100 mbits.
To calculate the theoretical maximum
Start with the 1500 packet size, add the 12 inter-frame-gap + the frame overhead ( 8 for preamble + 14 for header + 4 for the CRC )
then calculate the theoretical max speed:
100 Mbit/s / 8 bits in a byte * (1500/1538)
= 12.19 MB/sec
The throughput will decrease when packets get smaller (the minimal ethernet packet would have 46 bytes payload @ 6,85 MBps).