Process Explorer is the best that I can think of, it should be able to give you performance graphs of the process.
One thing to remember, many AV type processes PL can not alter these process so keep that in mind. Any I/O from them is best to handle it another way.
The best thing I can think is to first try lower CPU priority of the process and see how results go, then try I/O priority.
You will just need to test as I can't think of any other way.
Here a possible example: (I have not tried this yet). I found searchindex.exe was running when I didn't want it to (I always thought these maintenance type processes are supposed to run in background only, idle times). So this process uses I/O to index files that get changed, it is a background type process and might work well with lower I/O but again I would try CPU priority first.
Above is just example of a process that might work, but as I mentioned above always try other ways, in this example for me I removed the games folders that had indexing set in indexing advanced settings, that stopped indexing running while playing those games.