The main difference between these two ASUS boards is just as you put it, support for CrossFire X/SLI. That's not really a big issue I am imagining for you, though personally for myself if possible I try to opt for the "What If" factor and get the motherboard that supports it just in case it is needed in the future. However, the 450 graphics card you are looking at will be plenty of power for what you need!
One thing to keep in mind, though, is that all fo the PRO series of motherboards from ASUS qualify for advance replacement in the case of a failure. This means if your motherboard goes out, they will overnight a replacement to you before you have to even send the faulty one back, which with other motherboards and vendors you would have to send the faulty one back and wait up to three weeks for a replacement. I've only had one ASUS motherboard go faulty in four years, but that would have been a nice thing to have. Still, it may not be worth the price difference between those two motherboards! That is why we ended up choosing the EVO series from ASUS as it is kind of that happy medium between the above to ASUS boards (but of course at the moment, newegg is sold out!)
The good thing I see with the boards you posted above, though, is that they both have built-in SATA 6Gb/s. Your Western Digital hard drives are native 6 Gb/s SATA3 hard drives so that just means you can use the full potential of the hard drives (and then some!) I have unfortunately had some bad luck with the USB3 drivers on a couple computers, but I believe slowly but surely those have been getting all worked out.
Given the rest of the components that you have selected out above (especially with a nVidia graphics card and 1600 Mhz DDR3 memory) I'd say your better bet here then would be the i5-760 processor. With the discounted price it's much more feasible as it approaches the same price for the AMD system. Also, did you notice that the ASUS boards have a discount if you purchase the combo with the motherboard and Core i5 together?
In the end, between this system on an i5-760 processor or an identical system on a Phenom II X4 955 you wouldn't be able to tell the difference performance-wise even having the two systems setting side by side. They are basically tied. If you ran a full suite of benchmarks and tests the numbers would be close and one might edge out the other just slightly but not in a way that you'd ever be able to recognize a difference in real world use.