Don't touch an 8600, there is much, much better around for the same money. Also where do you get your 9800GTS info from?, I have seen nothing on that. GPU wise, we need to know what monitor you have?
Regarding the E8xxx series, they would be nice to get but they are hard to get hold of at the moment, not to mention the fact as a result, they are more expensive and are not the same price as their replacements currently. Oh and I'm fairly sure Retail Warranties don't cover OCing.
Those cases you mentioned are good but aren't exactly cheap, and would use up a sizeable amount of a £500 budget. The Antec Sonata case mentioned is good a bet though especially as it comes with a more than good enough PSU.
And really you should always get a DVD writer, they are so cheap now, there's only perhaps a few £s difference between them and just a normal combo DVD/CDRW. As an example, I got my Samsung 20x DVDRW (with Lightscribe) for just £16 in December!