Bigram
There are several factors that could be at play here. If the system is running good with other apps perhaps the HD speed is one area where you can start to look into.I made the move to SSD and my start times have dramatically reduced and overall speed is up quite significantly.
If a SSD is not an option, try installing 5.5 or 6 and see if you are seeing the same issues.
Let me know how you make out.