Why is my SSD so slow?

[Daniel1]

Trying to troubleshoot performance problems (stuttering audio) I came to notice issues with disk I/O on this system: high CPU usage during disk transfer (32.7% - 47.5%) and low transfer rate of the internal SSD (42.6 MB/s).
Both metrics puzzle me. The internal SSD is only 1.3 times faster than the external disk. Also, it is only 0.6 times the rate of a netbook. Finally, the CPU load seems excessive.

Is my SSD too slow? How to fix this? Could this contribute to the original issue of stuttering audio?

I am using ThinkPad X220 (4291-8Y4).
The following tests were run with McAfee on-access scan active. Comparing internal SSD with external HDD (via USB 2.0) and with Asus Eee PC 1005. Used HDTune Pro (http://www.hdtune.com/download.html) to measure transfer rates.

X220, internal SSD
HD Tune Pro: TOSHIBA THNSNC128GCS Benchmark

Test capacity: 100 gB

Read transfer rate
Transfer Rate Minimum : 31.3 MB/s
Transfer Rate Maximum : 211.3 MB/s
Transfer Rate Average : 42.6 MB/s
Access Time : 0.251 ms
Burst Rate : 208.4 MB/s
CPU Usage : 47.5%

X220, external HDD
HD Tune Pro: WD My Passport 0740 Benchmark

Test capacity: 100 gB

Read transfer rate
Transfer Rate Minimum : 29.2 MB/s
Transfer Rate Maximum : 32.8 MB/s
Transfer Rate Average : 31.4 MB/s
Access Time : 12.8 ms
Burst Rate : 32.9 MB/s
CPU Usage : 32.7%

Comparing with Asus Eee PC 1005, Eset on-access virus scanner enabled
Asus Eee PC 1005, Internal HDD
HD Tune Pro: ST9250315AS Benchmark

Test capacity: 100 gB

Read transfer rate
Transfer Rate Minimum : 58.5 MB/s
Transfer Rate Maximum : 77.3 MB/s
Transfer Rate Average : 71.0 MB/s
Access Time : 14.0 ms
Burst Rate : 109.1 MB/s
CPU Usage : 4.9%