vCPU speed setting is what is the max speed of the cpu. If set to 0.26 Ghz - you are going to have a slow cpu.
The reservation % - is where things get odd.
Lets say we set the vCPU setting to be 1.799 Ghz (I always set to the same as a full cpu or you will have waste)
If you set the reservation to 10% that means you will under contention have 180 mhz to use (minus schedule issues that happen - cpu ready time for example can kill a system even with reservations on cpu)
Also keep in mind if you use ePVDC's this 10% value is what is used to calculate placement, not the real system load (I still wish this could be configured). This can cause issues if you have unbalanced ePVDC's. (Also to note unless you have very small memory footprint hosts this placement will drive off cpu not memory most the time, causing this % number to be very important to get right for the load that will be in the OrgVDC)