I have yet to play with the beta of Drupal 8. Any good?

I have messed about with Concrete5 now for perhaps 20-30 hours total. Its nice. Very nice in fact. Some UI stuff imho needs some surgery. Sorta like alot of other things.
Concrete5 on a Windows Xampp box when having sessions thrown at it (a Dual Core 8500), 16GB Ram, 7200 RPM HD, faired "fair". I'd not expect it deal well with significant traffic on a shared host.

When moved to my Core i3 Lenovo server (32 GB Ram), Has All Samsung 850 SSD's in it (4 of them presently), 2 for .NET IIS, 2 under Linux/Apache/PHP/Mono a 2TB HD for backup and/or DB.

Faired MUCH MUCH better. It on a SSD VPS or Dedicated server is a very viable option.

On my Dell rack server (not in rack) 64GB Ram which is a dual quad core CPU with two SSD's and 15,000 RPM TB drives. it did well. On SSD, just fine, on HD, not so much. I enabled our smart cache Apache module on this box and was blown away, almost a 950% increase in performance. I shouldnt be "that" surprised as it has ALOT of files. Its actually a pretty strong CMS system.