How to identify if my Mac is running slow or is just over the hill? I have a 3 year old 15" 2.4 GHz Intel Core 2 Duo MBP that I upgraded to 4 GB of RAM about a year ago.

Before I made the switch to Apple I used to feel the need to upgrade my Windows based laptops every 3 years, that's about when they started to feel sluggish.  After paying double what I would pay for a Windows machine, I'd hoped I might be able to squeeze a bit more life out of my Mac, maybe 4 years.  But it's coming up to its 3rd birthday and it's starting to feel a little sluggish at times.  In fairness, it is mainly when using apps like iPhone 11 and Final Cut Pro X.  

I replaced the 250GB drive in it with a 500 GB 7200 RPM hard drive about 18 months ago, so I sometimes wonder if that could have introduced a problem that might be causing it to run slow.

So my question is: is there a way to test the HD, RAM or other things to see if there's a problem with my setup that could be easily fixed, or am I just expecting to much of my machine?

Anthony
I can't say the drive would have caused issues, as MacBook Pro models form 3 years ago came with 5400rpm hard drives. What does your system say in Activity Monitor? Any additional overhead in CPU or Disk I/O? If it's just system strain, and you have the appropriate amount of RAM, a SSD is the only additional upgrade that comes to mind.