Your stated goal is to improve aspects of the application performance (loading time, etc.) I have similar issues in other languages (C#, C++, C, etc.) I suggest that you focus not so much on the timing measurements that the Flex profiler gives you, but rather use it to extract a small number of samples of the call stack while it is being slow. Don't deal in summaries, but rather examine those stack samples closely. This may bend your mind a little bit, because it will not give you particularly precise time measurements. What it will tell you is which lines of code you need to focus on to get your speedup, and it will give you a very rough idea of how much speedup you can expect. To get the exact amount of speedup, you can time it afterward. (I just use a stopwatch. If I'm getting the load time down from 2 minutes to 10 seconds, timing it is not a high-tech problem.)
(If you are wondering how/why this works, it works because the reason for the program being slower than it's going to be is that it's requesting work to be done, mostly by method calls, that you are going to avoid executing so much. For the amount of time being spent in those method calls, they are sitting exposed on the stack, where you can easily see them. For example, if there is a line of code that is costing you 60% of the time, and you take 5 stack samples, it will appear on 3 samples, plus or minus 1, roughly, regardless of whether it is executed once or a million times. So any such line that shows up on multiple stacks is a possible target for optimization, and targets for optimization will appear on multiple stack samples if you take enough.
The hard part about this is learning not to be distracted by all the profiling results that are irrelevant. Milliseconds, average or total, for methods, are irrelevant. Invocation counts are irrelevant. "Self time" is irrelevant. The call graph is irrelevant. Some packages worry about recursion - it's irrelevant. CPU-bound vs. I/O bound - irrelevant. What is relevant is the fraction of stack samples that individual lines of code appear on.)
ADDED: If you do this, you'll notice a "magnification effect". Suppose you have two independent performance problems, A and B, where A costs 50% and B costs 25%. If you fix A, total time drops by 50%, so now B takes 50% of the remaining time and is easier to find. On the other hand, if you happen to fix B first, time drops by 25%, so A is magnified to 67%. Any problem you fix makes the others appear bigger, so you can keep going until you just can't squeeze it any more.