@Spyder4G 

The numbers look like 4G network LTE bands.

Which band is the best depends on your 4G network operator. You may want to try setting a band manually and then check what is your download and upload speed for a given band.

Band 20 has usually best coverage outside big cities but the lowest data rates.

Band 7 is likely to have the best data rates (fastest internet) if the signal is strong enough.

Band 3 is a good compromise between bandwidth and coverage.

List of the bands is here:

LTE frequency bands - Wikipedia

Most often it is best to leave it on auto - the modem/router should select best band based on signal strengths and other parameters. However, if Auto selects band 20 and the internet is slow, if you can manually connect to band 7 or band 20 the internet connection might be faster but at the same time less reliable.

  @PetrF 

Thank you for the detailed explanation.

Based on that, I made various speed tests for each band and band combination, here are my results:

From what I can see, the fastest bandwidth is achieved with the band combination 1+3, at least for my location and provider. Are my results within the expected 4G+ network speeds?

Thank you.

PS:

Today band 1 appeared, strangely that wasn't there a few days ago.

PS2:

You'll notice there are no values for band 7, thats because I get no service from that band!

  @Spyder4G 

I think it looks good and the carrier aggregation seems to work for you, which is also good.

Just the result in band 20 for Fast.com does not make sense. If this is not a typo it might indicate that the signal is not strong enough or the LTE network in the band 20 is highly loaded with traffic and the data rates are unstable. 

The aggregated data rate might be limited by the network operator to 100 Mb/s and this might be the reason why any of the aggregated rate did not exceed 100 Mb/s.  

You can check it with a smartphone that supports LTE+. However, be aware that for most of the recent smartphones the achievable data rates are much higher than for Cat 6 modem as the smartphones are Cat 9 or even higher. 

If the modem shows signal strength (RSRP) and signal quality (RSRQ) you might want to compare values described below and decide if an external antenna might improve data rate or stability for you:

RSRP:

>-90 dBm - Excellent

-90 dBm to -105 dBm Good

-106 dBm to -120 dBm   Fair - better antenna might help

<120 dBm Poor - good antenna will help 

RSRQ:

>-9 dB - Excellent

- 9 to -12 dB Good

< -13 dB not Good - good directional antenna is likely to help to reduce interference

I do not have the MR600 myself so I cannot provide any model-specific information. I am in the process of shopping for a replacement for my old Zyxel and MR600 is one of the candidates. 

  @PetrF 

About band 20, it is not a typo mistake, I run the fast.com test a few times and it always came up at a max 2Mbps. Nothing to worry about since the other bands worked fine.

My modem shows the following values:

Based on your notes, my RSRP is "good" and my RSRQ is also "good". So good overall

Thank you for your help. I hope others will find this information useful while configuring their modems.