Great advice everyone, AVSIM is the place to come!! I think I sorted out the problem/s now.
After finding lua5.1.dll in an Orbx folder and putting it back into Windows, my problem with FSX hanging on the task bar is solved. After leaving the PC to defragment today, while at work, I've checked my loading times and the results are striking.
FSX used to load at 5:45 mins after my two new Orbx regions were removed, today it loaded in 1:50 mins! That was straight after a fresh PC boot-up. Coming out of FSX and going back, the game loaded in 55 seconds. Now we're talking!!
I'll reinstall my two Orbx regions and then record some new loading times. All is well