If you really wanted the option for crosfire i would probably get a 750tx, i have no doubt that your 650tx would run them fine, but depending on how many other components, fans, etc it can get close to the max wattage, its usually better to have a some headroom. With that in mind, if you know you are no going to get alot of that stuff you will be fine, i run a i7 overclock at 3.2GHz, asus p6t, 6gb ram, gtx 285, x-fi fata1ty off a 550w seasonic pretty easily.
As for the cards, 40 euro is not really worth the upgrade, sapphire is a great brand also, its just that XFX has great tech support and a great warranty, if the price difference is a lot go with the sapphire. The 4890 is a good 5-10% better and has nice overclocking capabilities so if you can get one for about 20 euro or less extra then it would be a good buy. If your playing at high resolutions then the extra 512mb would be worth it.
As for the cards, 40 euro is not really worth the upgrade, sapphire is a great brand also, its just that XFX has great tech support and a great warranty, if the price difference is a lot go with the sapphire. The 4890 is a good 5-10% better and has nice overclocking capabilities so if you can get one for about 20 euro or less extra then it would be a good buy. If your playing at high resolutions then the extra 512mb would be worth it.