What J said. The ratings ranges are too big to predict. The ratings difference could be as little as .01, 4.49 vs. 4.50, or it could be as large as .99, 4.99 vs. 4.00. That’s a huge difference. In addition, you have the variable of style match ups. It’s possible that, in the first scenario, the 4.5 would win the majority of the matches.
That said, the average level 5.0 will straight set the average 4.5 easily, typically in the 6-0 to 6-2 range. If the 5.0 is having an off day or the 4.5 is en fuego, it could be competitive. Otherwise, it should be an easy day at the office for the 5.0.
Still, style match ups can matter quite a bit with one level difference. I’m a former 5.0 playing at a 4.5 level now due to age. When I play 5.0’s that try to hit through me or that use spin and depth as their big weapons, I’ll still give them fits. If they just run me side to side, short and long, I don’t last a set before my level drops off the table.

(There is a reason the senior tour plays one set matches)