If fuel cost and fuel efficiency were not the issue, what is the maximum speed (air speed and ground speed) that business jets or airliners could travel at without exceeding the maximum noise and sonic boom allowed or as regulated in the USA, Europe and the rest of the world. I need to know why there are no faster business jets and for business class airliners given that private and business fliers are prepared to pay a premium
Business jets are developed to different rules than airliners. The biggest difference is that, indeed, fuel price and fuel efficiency are not an issue when what counts are bragging rights for the fastest plane on the ramp. Their speed has steadily increased and is now at Mach 0.935 for the fastest models. Compare that to Mach 0.78 to 0.85 for regular airliners.
Supersonic business jets were proposed several times in the last decades, but so far nobody has risked to spend the money it needs to bring one design to a type certificate.
Since supersonic flight over land is heavily restricted, the fastest speed would be Mach 0.99. However, since the speed of sound decreases with increasing altitude in parallel with air temperature, what is Mach 1.15 in 40.000 ft becomes only Mach 0.998 on the ground, so the shock will disappear close to the ground. If the goal is to avoid the shock on the ground, flight speed high up can very well be mildly supersonic. However, this will place the airplane close to its drag maximum, giving it exquisitely poor efficiency for a small gain in speed.
It is 0.99 Mach over land. I don't see any restrictions over the ocean. Based on the top answer to this aviation SE question, I think if you can design a more stealthy hypersonic transport aircraft and fly it at high enough altitudes in the stratosphere, you may minimize the sonic boom to the extent that it is a non-issue. The NASA graph in the answer shows that the XR-71 has an insignificant sonic boom when cruising at 60,000 ft MSL compared to the Concord SST.
Ram-jet technology would eliminate the need for the turbine compressor used on current jet engines thus allowing the aircraft to be quieter and more streamlined and stealthier.