..what difference can I expect such as speed and ease of ride from a premium grade bike.
There's a saying about "the law of diminishing returns". In this case meaning that as you progress, each fraction of improvement will cost more and more to achieve.
And of course the quote, I think from Greg Lemond."it doesn't get any easier, you just go faster".
The difference in top and average speed a rider can expect to gain from going from a properly fitted and fully functioning mid-range bike to a properly fitted and fully functioning top-end bike is small, single-digit percent.
The difference in ride enjoyment a rider can expect to gain from going from a properly fitted and fully functioning mid-range bike to a properly fitted and fully functioning top-end bike can not be measured.
I have heard that a budget bike has got open ball bearing system vs sealed bearings...
Nah.
In strict mechanical terms an "open" bearing would mean one where you can see straight into the balls and the races.
I've seen a grand total of ONE such bicycle. Athough I've heard that track bicycles may sometimes be like this as they're generally ridden indoors and don't have to worry much about beearing contamination.
The huge majority of bikes have - from the perspective of definitions - sealed bearings, one way or another.
Quite often people use "sealed bearings" when they actually mean "cartridge bearings". Cartridge bearings, the
kind used in bicycles are usually sealed, which is
why they're used in bicycles.
Doesn't mean that your average cup & cone bearing is unsealed.
Unsealed bearings - whether cup & cone or cartridge - are quite impractical for use on a vehicle exposed to weather and contamination. Unless the bearing sits is a housing of sorts to protect it from dirt and water.
Anyone blaming a loss, or contributing a win to the
type of bearings used is not to be trusted. At least not on
that statement.
..which makes a difference in speed....
Only because something is true doesn't guarantee that it's important.
Bearing drag is only a few percent of overall drag, with air drag being the main contributor. So unless the bearings on your current bike are verging on seizing, switching to bearings with less drag are only saving you a few percent of a few percent. The difference won't rock your world. How you tuck your head at max effort, tire type, tire pressure, will be more important.
.. I am referring to crank, front and rear wheel bearings....
Of these, crank bearings are probably the least important, as they turn the slowest. Then comes the front wheel bearings as they carry the least load. Of the tiny importance it might have, the rear wheel gets priority. it spins faster than the crank, and carries more weight than the front.
But again, this is all chasing tiny, tiny improvements that may not even be measurable under real-world riding.