If you have a processor with multiple cores (dual-core, quad-core, etc.) then you should open multiple clients and assign them to different cores.
To do that:
1. Open task manager (ctrl + shift + esc)
2. Click the 'Processes' tab
3. Find the bots in the processes list (either *********, Javaw.exe, or something about Nexus, not 100% sure as I've never used Nexus)
4. Right click one of those processes, click set affinity, and make sure you either have core 0 or core 1 checked (for dual-core processors. for quad-core there should also be core 2 and core 3) then press ok.
5. Repeat the fourth step for the other client, instead checking the other core and pressing ok.
Basically what this does is allows your processor to spread the CPU load out more by splitting the task into two parts.