For boot time - stopwatch only device and is broken down into 2 parts. (1) the Time it takes the bios to load then (2) the time it takes the operating system to load.
For program load time, yes you can probably get a grogram. It would get computer time at start of load and then computer time when program completes loading. t sub 1 - t sub0 = load time. Bear in mind this is more a function of the HDD performance than it is the CPU (HDD being the slowest device. HDDs are in millseconds and CPU in nanosecounds even picoseconds. multiple programs competing for HDD access can bring the computer to its knees
Programs generally be come unresponsive when you run out of memory. They will slow down at the Higher CPU utilization - at what percentage CPU utilization does the program slows down consiserably is based on progam priorities determined by the program/operating system. A good test would to be to use a high priorty program that you can vary the CPU utilization (for an E6400 I used Intel's TAT program) then simply run your program and you WILL KNOW when response is unecceptable.