Will I improve anything by going from 250 to 750 Mbps?
Unlikely. Your current speed is already way more than enough, assuming your bandwidth isn’t shared by a lot of other high demand devices.
Are you having a problem making you think you need a faster connection?
I run on 70 Mbs internet down a phoneline. The company that did supply me with a 250 Mbs then couldnt keep a flat response graph at those speeds due to bad lines turned out to be a lot worse than the service I use now.
I flew MSFS 2000 on a 56k modem, so I am thinking the max bandwidth for this will be around the 5 - 10 Mbs as its never gone out of that range with live data and sattelite settings on.
Do an MTU check on what you have now, Im saving a fortune