Okay, clearing space on C Drive and increasing virtual memory to double that of physical memory has made no difference.
The amount of terrain detail and complexity in a scenario or map makes little or no difference to the RAM issue but can effect FPS
It is the RAM issue causing the drop outs and stuttering rather than an actual drop in FPS.
Use of Ram seems to hover between 6.5GB and 7.5GB. When it goes above 7.0 is when drop outs really start. After a scenario has been run, it will stay at this high usage in all game menus and when Alt Tabbed out of SB and will not fall away until SB is terminated