I agree with Brant but your EF lenses will be useful for years to come as the EF to RF adapter works flawlessly. Even the EF-S lenses can be used with the R5 in 1.6 crop mode.

The cost of replacing my collection of EF lenses was the primary reason I held out for the R5 as opposed to switching to Sony.

I believe the R5 currently compares well with the performance of the 1DXIII and the technology will advance.

Also the lineup of RF lenses will grow and there will be options that may eventually make you want to switch over to some of the RF line.

In that regard I did purchase the 800mm f/11 and the 100-500mm RF lenses.