The WEI is not a good benchmark.
If you what a more accurate benchmark use HD Tune
or Crystal Disk
. AS SSD Benchmark
is a good one for SSDs.
It will also depend on the specs of the HDD and SSD. An older SATA drive may not be able to directly use some of the benefits.
A WEI of 5.4 tells me it may be an older model or have other issues. A 'Green' version uses less power and has less performance.
For the best performance get a 7200 RPM, 32 MB cache, HDD. Be sure it is SATA 2 and supports NCQ, S.M.A.R.T. and Plug and Play.
There're other benefits like NCQ Native Command Queuing, will get the data faster with less wear on the HD. Plug and Play, if you need it, ie external HD. As mentioned earlier.
The best benefit with a SSD is AHCI will enable Trim when using Windows 7.
Some SSDs will seem to have better specs but will get lower benchmarks and WEI score due to the I/O rates.