The best way to find out what is actually happening within your system is to use Bill Gehrke's PPBM8 testing setup.
You download his zipped testing folder, install the monitoring applets included, load the included project file into PrPro, and "export" ... all following specific instructions. Upload all the resultant log files, and you get back a very specific report ... GPU and CPU performance, read/write performance, everything. Doesn't take too long to do and gives very concrete results.
Since you are a big G-RAID user are you Mac Based? PPBM does not support Mac. If it is PC what is the computer interface to the G-RAID?
Thanks for the attempt but yes I'm Mac based. Appreciate it!
Sent from my iPhone
Run some tests on your G-Raid's to see what the performance really is
A Mac with Premiere and a G-Raid should work just fine.
How much disk space is free on your Macintosh HD? If it's less than 10%, that could be an issue. Try to keep at least 20% of the boot drive capacity free at all times.
How much disk space is free on you G-Raid? If it's less than 10%, that could be an issue. G-Raid will tell you that you can go up to about 95% capacity and not lose bandwidth, but I'd still try to keep at least 15% to 20% free.
How is the G-Raid connected to the iMac? You may already be aware that Thunderbolt or FireWire are your best choices.
What are your Energy Saver settings? Make sure that the drives are not going to sleep.
Have you run Disk Utility recently? If not, run it on all of your drives and repair any issues that may be present.
Have your run Repair Disk Permissions recently? If you're running a recent version of macOS that does not allow you to do this, consider purchasing TechTool Pro for this.
What anti-virus software are you running? If nothing, Sophos Anti-Virus for Mac or Malewarebytes are good choices (and free).
If none of the above helps, create an external boot drive with just the macOS and Premiere Pro installed to test for a software conflicts.