Ridiculously slow write speeds in Laptop Hard Drive. Please advise.

Try running CrystalDiskInfo and HDTune on your drive first. There may be other problems with the drive which aren't showing up in the speed benchmark. CrystalDiskInfo will query the SMART stats on the drive which flag common problems and errors. HDTune will run tests over the entire drive (or at least those parts with free space) instead of just a single location, and can find slowdowns due to certain portions of the drive experiencing problems.

https://crystalmark.info/en/software/crystaldiskinfo/
http://www.hdtune.com/

Write caching is generally a bad idea since it can lead to permanent data loss in the event of a crash or power failure. This may be less of an issue for a laptop, since it has a built-in battery backup. Windows has a built-in write cache (writes are stored in RAM, then pumped to the drive as quickly as the drive can handle it).

http://www.thewindowsclub.com/enable-disable-disk-write-caching-windows-7-8

The first check (enable write cache) doesn't offer much speed unless you're writing a bunch of small files at once. The second one (disable write cache buffer flushing) is the big speed improvement. It allows data to remain in the write cache (RAM) until the disk is free to accept more writes. Normally the cache is flushed (emptied and written to disk) at short intervals to minimize the data loss in the event of a crash or power failure. But by disabling this periodic flushing, the computer doesn't have to wait for writes to finish before continuing on with other tasks. It comes at tremendous risk to your data though, since a power failure or an OS crash will mean you lose any data in the write cache. So think carefully before you enable it.

If you're open to replacing the HDD, a SSD will provide a huge improvement in speed (tens to hundreds of times faster at small file read/writes). If a SSD is out of your price range or if you need the larger capacity of a HDD, you can look into hybrid drives (SSHDs - solid state hard drives). They're a regular HDD coupled with about 8 GB of flash cache. The flash operates at near-SSD speeds for reads (writes are still constrained by the speed of the HDD), and are very effective for frequent operations like booting your computer. It'll probably drop your boot speed to the same as a SSD. I would avoid the WD SSHDs though because they have a different issue with short head parking timers (shows up in your laptop as microstutters if it's your only drive - e.g. screen and mouse freezing for a split second every 10-15 seconds). As best as I can tell, all 5400 RPM WD drives suffer this issue.

However, if my guess is right and your slow boot times are due to driver load errors causing long waits for timeouts, then even a SSD isn't going to fix it. In this case the computer would be slow because it's literally stopping and waiting during the boot process. It's not being slowed down by a device. You'd have to locate and uninstall/reinstall the problem drivers. Often it's easier just to reinstall Windows. (There's also an off chance that it's a hardware failure elsewhere in the computer causing the timeouts.)