As mentioned before ready time is the sum for all CPU's.
So if you have 40% ready time on a 10 vCPU VM, this means that each vCPU had to wait around 4% of the time of the interval to be scheduled on the processor. The 5% and 10% rules apply as PER vCPU and not the total amount. So it's important to not misinterpret the values you are looking to.
Interval is also important
An excellent post I use as reference a lot of time can be found here
http://vmtoday.com/2013/01/cpu-ready-revisted-quick-reference-charts/
What kind of hardware do you have ? Intel-based with HyperThreading or AMD?
I did some testing with VM's using 100% CPU on HT Intel machines, what I noticed, as soon as I passed the physical 16 core boundary (ESX host had 16 pCore / 32 logCore with HT) the ready times went up and became CPU bottlenecks the more VM's I put on it. This only as applicable if you all want to use the CPU cores at the same time :smileyhappy:. In our normal environment we have a ratio sometimes to 1:4 without high ready times because most machines don't use so much CPU on daily bases.
Try to map the logical cores/physical cores with the amount of vCPU's.
Do you use any affinity rules ? If set wrong this can negatively or positively impact your ready times.