It didn't occur to me until after posting the above that I needed to consider Jumbo Frame support on the switch. It's an unmanaged Netgear switch. According to their support site any with serial numbers starting 1E3, 1R4 or 136 support them. But mine starts with a 2, so I have no idea. Guess the only way to tell is to turn them off on my network card and see if it makes a difference.