Leon,
Don't waste your time mucking around with upgrades, there will always be a weak link in your system and you may not benefit fully from the upgrades.
Keep your monitor etc and get a new box with new bits. You will have an extremely better computer that is better matched and overall better performance.
If you are doing astrophotography processing on your computer then you will benefit from this. If you can afford it, get the SSD main drive and a WD black secondary for your data, (these cream the other WD drives for an extra $19). Otherwise just get the WD black as a main drive.
P.S. I have read many of your posts and the issues you have had with computers, do yourself a favour, you will not be disappointed.
All the best.