Honestly, I would say the graphics card is the most likely bottleneck, get a new one and see if you're happy with the performance (though it may not get you to Ultra).
If you're still not satisfied then look at replacing the CPU, motherboard, and memory, with your already purchased gfx card.
If you are happy then you've not wasted cash on components that you didn't need. Plus, in the future if you aren't happy with performance it is likely that the components available then are faster and/or cheaper and make your money go further.
It's an approach that has worked for me so far, and I'm still running a Q6600 quite happily. and if you get free delivery there really is no reason to splurge all at once to save costs.