The modem could be part of the issue but you would need to check with your modems user guide and check what technology is supported.
Wired will always give you the fastest. For older machines they might be limited to approx 100Mbps.
Your modem may have settings for both 2.4GHz and 5GHz (check with the modem model online or via your user manual) each have pro's and con's.
Real World Speed
3 - 32 Mbps
10 -29 Mbps
433 Mbps - 1.7 Gbps
210 Mbps - 1 G
I myself like to name each Wifi Network seperatly (i.e Your WiFi 2.4ghz & Your WiFi 5ghz) so if you see the 5hz option you know that your connected to the fastest available option to you, Some modems do not support this feature.
(I am not an employee of Vodafone New Zealand and i am not associated to the social media team. I am a regular Vodafone New Zealand customer that volunteers my time here to help make Vodafone a better place for all)