Before I say this, I want to repeat that I am all for effective upscaling, the option of more performance (for possible visual impact, although this impact is decreasing) for more people is only a good thing. However, to note the impact of RT on framerate, follow this method.
Step 1 - Select benchmarking game
Step 2 - Enable RT
Step 3 - Play for a couple of minutes
Step 4 - Note average frame rate.
Step 5 - Same as steps 1-3, but disable RT
Step 6 - Note average frame rate.
Step 7 - Compare figures from step 4 and 6
Additionally, this test will also provide happiness levels.
If step 4 is higher than your desired framerate, success! You may have a Good Day.
If step 4 is not higher than your desired frame rate, oh dear. You will need a new GPU for RT. This can cost HUNDREDS. You will probably have a Sad Day.