My HDD is "Underperforming"

To be quite honest, it's probably just due to the fill rate, but I just want to be sure.

I have two Western Digital Black Performance 6 TB Drives. (More storage than you need is always a good thing)

And these drives are fast. Extremely fast for Hard Disk Drives. Without a cache they read/write at about 230 MB/s.

HDD_0: 950 GB / 5.5 TB Used - 190 MB/s Read and Write Avg.
HDD_1: 100 GB / 5.5 TB Used - 235 MB/s Read and Write Avg.

I figured this out when using a benchmark on the rest of my computer.

Anyways, I keep my PC clean, up-to-date and fast by:
- Windows Disk Cleanup (For those pesky Update files)
- CCleaner (Internet Junk)
- Driver Booster 6 (Drivers)
- Power Profile: Highest Bitsum Performance (Aggressive Turbo)
- Advanced System Settings: Highest Performance (Disabling Aero effects, etc.)
- Windows Drive Optimization (TRIM + Defrag)

I don't know if maybe I am missing anything else? I am only concerned because if every 1/5 of drive utilization costs 40 MB/s, it will be a really slow drive when I max out at 80% utilization.

That being said, I don't think the Allocation Unit Size was modified to a higher amount.

RAM Caching usually is on for the drive, I turned it off for benchmarks.

The only other thing I can think of is a bad SATA cable, but I've never had problems before. When I had it at about 500 GB used, it was performing normally.


The benchmarking program I used to figure this out was Userbenchmark, though I did double check in CrystalDiskMark to only confirm the loss in speed.


Thoughts?
 
Solution
it will get slower once u fill it up, speed is variable, outer edge of platters is fastest, inner rings are slower

run hd tune to see your full drive speed, not just some random tiny part of it



Read transfer rate (D)
Transfer Rate Minimum : 102.3 MB/s
Transfer Rate Maximum : 249.8 MB/s
Transfer Rate Average : 190.7 MB/s
Access Time : 12.1 ms
Burst Rate : 302.3 MB/s
CPU Usage : 1.4%

Read transfer rate (E)
Transfer Rate Minimum : 112.1 MB/s
Transfer Rate Maximum : 257.5 MB/s
Transfer Rate Average : 195.0 MB/s
Access Time : 12.2 ms
Burst Rate : 232.5 MB/s
CPU Usage : 1.0%


Thanks for the software, it appears D: is actually 10 MB/s slower than E: