Ok, just managed to get it working. After installing, I couldn't start it. Signing out of the CC desktop app and signing back in sorted that out.
When it started, It was a lot faster than ver 5.7. It caught me out and instead of converting my existing catalog, I pressed to create a new one. Bugger. What to do then. I opened my folders list to see which files were new in the catalog location. Shut down LR6 and then deleted the new catalog I created by accident. I restarted LR6, it asked for the missing catalog, I navigated to my LR5 catalog, selected that and it asked to convert it. Having optimised and backed it up already I went ahead and converted the catalog. A couple of minutes perhaps and I ended up in LR6.
First impressions? FAST!
The previews were finally snappy, loading almost instantaneously. Looking through the preferences, I see there is a new Performance Tab. I had a look in there and see my Quaddro k2000 graphics card is detected and selected. Finally, the cards GPU is being used by LR. The older versions didn't and the performance took a bit of a hit I found. My machines mb may be 5 yrs old, but, I have fast ssds as working and scratch drives along with a fast raid as my data drive. With 24 gb of ram and no games etc, the machine is reasonably speedy still until the cpu itself becomes the choke. This was happening with the older versions. Now, my new GPU is doing the work in the develop module but the overall snappiness of the system now is remarkable. Barely scratched the surface but the difference so far is impressive.