I tried mining in a pristine metallic ring today (27-01-2018) in both 3.0 and the current release of ED. In both cases I used my mining Python which has only 64 ton of cargo space. My impression is that it is improved in 3.0. One new and worthwhile feature in 3.0 is the ability to tell the collectors to ignore a certain material (and to revert that decision if required).
I did find in 3.0 that there was less Indite, Gallite and Bertrandite around and more of the precious metals. There was some around but I very quickly found metals. It could have been the ED RNG gods but it did not feel like it. In fact in 3.0 I filled all my cargo hold up and filled up all the slots (bar one) in my refinery with 100% refined ore( so I effectively received an extra 9 tonnes.) In fact I could throw what little Bertrandite, Indite and Gallite I did collect away and the cargo was soon filled up
The test was not perfect as I tested in a different ring in both versions but my impression was that in 3.0 was it was much quicker to fill up my cargo hold with metals and there was less Indite, Gallite and Bertrandite around and more Samarium, Praseodymium and Osmium. There's also the added bonus that low value materials can now be ignored (although I did not realise this at first). I did not find any Pain-in-the-arse-ite in either case.
By contrast, in the current version of ED it feels like you have to hunt for rocks that contain any metals in reasonable quantities and they are usually only found in patches.