When you're doing ... ?
Your system info .... ?
Disable the GPU in LR / Prefs / Performance
Thanks for the input guys.
Disabling the GPU has worked so far - but I thought one of the points of LR6 was the performance benefits?
Info posted below:
Lightroom version: 6.0
Operating system: Windows 8.1 Home Premium Edition
Version: 6.3 
Application architecture: x64
System architecture: x64
Logical processor count: 8
Processor speed: 2.1 GHz
Built-in memory: 8061.2 MB
Real memory available to Lightroom: 8061.2 MB
Real memory used by Lightroom: 324.8 MB (4.0%)
Virtual memory used by Lightroom: 288.5 MB
Memory cache size: 58.3 MB
Maximum thread count used by Camera Raw: 4
Camera Raw SIMD optimization: SSE2,AVX
System DPI setting: 96 DPI
Desktop composition enabled: Yes
Displays: 1) 1366x768
Input types: Multitouch: No, Integrated touch: No, Integrated pen: No, External touch: No, External pen: No, Keyboard: No
Graphics Processor Info:
Intel(R) HD Graphics 4000
Check OpenGL support: Passed
Version: 3.3.0 - Build 10.18.10.3958
Renderer: Intel(R) HD Graphics 4000
LanguageVersion: 3.30 - Build 10.18.10.3958
Thanks for the input - although LR6 thought it could use the GPU (it had enabled the option) seems to work best without it enabled.
Onwards and upwards......