It all depends on how you define things.
So first the ISP router would need a port that is likely 5g to be able to run 3g. It likely will drop to 2.5g to match your router.
So lets assume you get past this. If you were to run the speedtest on the speedtest program embedded in the router you would likely see 2.5g or at least some number close. You can't get the 3g because the 2.5g port limits you.
Your problem is the lan port are only 1gbit. So even if your pc has 2.5g it will drop to 1gbit between the router lan and your pc. So at most you could run 1gbit.
Now if you were to hook up 3 pc at 1gbit each they in total combined could use the 2.5g internet. This is where it depends on how you define stuff. Is it a single machine running at that speed or is it multiple. Pretty much the same lies you see on wifi where they add the speed of the 2.4g and 5g radios together.
You would need even a more expensive router that has multiple ports that are 2.5 or faster. That way you could plug 1 into the ISP and a second one in the PC.
In addition these really high speeds are really only useful for downloads, they make no difference for most other applications. What you will find is many sites say like steam place artificial limits on the download speed. So even if they could technically allow you to download at 10gbit they will download at a slower rate. The reason you see stated is to prevent a small number of users with very fast connection being able to block the servers for other users. I know that I seldom see anywhere near the 1gbit speed I am suppose to get.
Maybe in your case you could download 2 different games on 2 different machines on different steam accounts and get over 1gbit total.
In general you have to really consider if you "need" internet that fast and all the hassles it involves setting it up. I was going to drop my internet off the 1gbit plan when the contract ended and the price increased but they agreed to extend it another year at the same rate. I still don't really "need" the 1gbit but the cost difference to drop to say 300mbps is only $5/month now.