In my next PC I'd like a CPU that will run a program that seems to max out the current CPU quite quickly, and makes the program show as "not responding" for a while.
When I look at task manager while running the program, the CPU usage is at 25% on a 4 core CPU. There is some usage shown in each of the core graphs, but it adds up to only the same as if one core were used.
Does this mean that to find a CPU that will be better at running this program I should be looking at CPUs that do well in single threaded benchmarks?
Yes, it sounds like you have a single threaded program. Choosing a CPU optimized for single threaded applications is appropriate. But also think about the rest of the system. A large on chip cache can help a single threaded program, as can the best memory timings. Xeon CPUs have a much larger cache than do the desktop Intel CPUs. The cost difference might be justified if this is a business application. Is this single threaded program doing a lot of I/O? Would a RAMDISK improve anything? If so then getting 16GB of RAM (or more) might be appropriate. Think about a balanced system for maximum performance