You will be able to try them, hopefully. On paper it looks to be a total badass lens, they claim that it is as sharp wide open at f/2 as the EF 24-70 II at f/2.8, that's impressive.
But not only is it the most expensive for a native mirrorless setup (ok, apart from the Sony 400mm), it is also probably the most front-heavy-feeling ever made amongst them.
What I mean is, when the lens is not that big but thick and weighs as much as this, it will feel even heavier (like Leica Noctilux lenses, which feel very dense) so it may become a bit shaky after a while using handheld, and there is no IS. That might actually matter a bit more in practice, than how sharp the lens can be.
The 11-24mm with an EF to R adapter is a pretty good "test-bed" for weight distributon before having this even heavier lens (but the range is more forgiving regarding usable shutter speeds)
The RF 24-70/2.8 IS may also be close to or just over 1kg, but that is quite a bit more manageable, it should be better than the EF 24-70 II as well, and the IS may also come in handy (for both photo and video), until they put it in the later bodies as well.