Yes, there is a difference. And, even though this difference is subtle, it is also incredibly important. In general, UPF 50+ protection will block more harmful UV rays than UPF 30 will block. However, to note, UPF 30 is usually in the ballpark of blocking around 97 percent of UV rays. Meanwhile, UPF 50+ protection can often prevent about 98 to 100 percent of UV rays.
Of course, more important than the percentage of any UPF protection is to ensure that it blocks both UVA and UVB rays.