It is €100 more, I don't think he will get GeForce GTX 770's...
To be honest I think it is worth the 100 extra. The lower thermals, lack of microstuttering, and comparable (if not higher) performance is worth it. The 7990 is not immune to thermal issues causing throttling. The 770s will also be significantly quieter than the 7990.
I think it's worth the extra (I don't know where you're ordering from, but in the US and UK 2x 770 are cheaper than 1x 7990, and I'm seeing GTX 770s for <350€) money. Microstutter is no longer an issue on AMD cards, but the sheer performance of the SLI setup is at least 1/7th better.