Are SSDs much much better than the SATA-II 3-Gb/s or 6-Gb/s, worth the extra pounds for much less capacity? I don't game, the pc is mainly for trading/everyday use, where the trading software is just like a hosted terminal...
depends, in your situation, probably not, but if you are running the OS and a few games off it you will notice the difference in load times and definitely benefit from it
Again like the other's said, I have an SSD on my laptop along with a SATA 3 Hard Disk, it is amazing for quick boot's and just program load time's, however if all your going to use it for is trading and basic web browsing it will not really benfit you, yes it will start up in a couple of seconds and may seem slightly quicker to respond. But in your case CPU and GPU upgrades would be more worth the cost than a SSD.