[nando4]

One thing I did notice last time I had the GMonster V4 in the system was that linux reported write caching disabled by default. Worth manually checking in WIndows (with hdparm) and switching write caching on:

hdparm -i /dev/sda
hdparm -W1 /dev/sda

Did you also do the Tony Trim as suggested in my previous post? If done those three things with no write performance improvement, then I'm at a loss as to what is the cause of the slower than expected writes.