The ET-16600 is the older model with officially lower ISO speeds (25 ppm black / 12 ppm colour), while the ET-16605 is advertised as a slightly modernised variant with higher stated print speeds (up to 32 ppm black / 22 ppm colour) and a recommended monthly throughput of around 3,300 pages. Otherwise, both devices are practically identical in terms of design, functions (A3+, duplex, ADF, EcoTank) and features.