Concerning the PSU: A sturdy PSU is an important part of the system, and you want to have a little wiggle room for extra power but 875 is beyond overkill for your system. Honestly the PSU you have now is even more than enough for what you have.
As for the GPUs: Do not crossfire if you are afraid of bottlenecking. If you plan on spending money on two 7770's, I would suggest you get a 7950 instead. It is an amazing card, and fits the pricepoint you plan on spending for upgrades. If you need any suggestions, It's your preference on the company, but the Sapphire Vapor-x 7950 is what I've been seeing topping the charts, and in some cases matching 7970s.
Your PSU offers no performance and can therefore not bottleneck your system, it can only put out so much power and could limit the components that you can run. In your case however a 650W PSU should be sufficient, provided it is performing up to its rated wattage, and to get two(2) HD 7770 just to test CrossFire seems like you have money to burn, in reality you typically get 150% the performance of one(1) graphics card when used in CrossFire and so it would probably be best to go with a higher performing card (HD 7870 for exaple). A likely bottleneck which you may not be aware of is your storage option, a Hard Disk Drive is far slower than a Solid State Drive and one can be picked up for a reasonable price.
If it were me, I would go the SSD route and if you feel you need more video performance go with a higher level graphics card.
Thanks guys! your comments and suggestions really helped. By the way, im using a WD 500gb caviar blue on my primary and another for my secondary storage. @noreaster did mention an SSD option, I'd note that.