Some users have recently had their accounts hijacked. It seems that the now defunct EVGA forums might have compromised your password there and seems many are using the same PW here. We would suggest you UPDATE YOUR PASSWORD and TURN ON 2FA for your account here to further secure it. None of the compromised accounts had 2FA turned on.
Once you have enabled 2FA, your account will be updated soon to show a badge, letting other members know that you use 2FA to protect your account. This should be beneficial for everyone that uses FSFT.
Definitely the SSD, you'll need at least 70GB to hit 300fps.
What settings, resolution are you using?
I would also say GPU, I'm sure a single solid card would do you better than 2 older 5770's, especially if you're concerned about solid fps with the extreme dips that CF can cause, combined with the natural game fps dives that can happen as well, I'd get rid of a dual-card setup if you are concerned with higher sustained fps.
The card is limiting but I wouldn't really call it limiting? Not being critical but I'm wondering what you would need 300+ fps for, I'm not aware of anything that can display even close to that unless there's a super CRT I don't know about..
Everything. You need at least 16GB DDR 2400 RAM to do predictive frame rendering allowing for over 300. A 4960x is need to then pre-process this frames and load the next textures. A PCIe 256GB SSD is 10x better than what you have now allowing for 10x the performance boost loading all this data.
Crossfire 5770? Srsly? Joke. Why do you not have a GTX 780 Ti or two?