Print jobs get transferred to the print server via the workstations server service request buffer, SizRegBuf . This buffer will have an effect on network performance in general. Increase the buffer in increments of 64 or 128 while print speed improves and other network access does not suffer. Unfortunately this is a twiddle factor. Be sure you can get back to where you started.

Hive: HKEY_LOCAL_MACHINE
Key: SYSTEM\CurrentControlSet\Services
Type: REG_DWORD
Name: LanManServer
Value: SizRegBuf