Increased ram to 1gb - and munin reports actually show some white space now.
For info of others who ask about minimum spec and performance, the server with 512kb was running fine serving about 20 CMS sites but when mail services were added it needed the extra memory most probably for the intense amavisd service. The extra ram has coincidently made web serving MUCH faster. Full spec as below on a vds:
250 MHz processing reservation though no limit on bursts
1Gb of ram