Fitting a Blu-Ray drive into such a small enclosure is going to be a *****! Like... really.
I think USB Blu-Ray is your best friend.
USB 3.0 is also pretty useless since all you'll get is faster transfer speed for now, unless you do transfer gigs worth of data daily. I'd just watch movies directly off the USB drive if anything.
And better specs come with heat and noise. You gotta consider that you have significantly less space to exhaust heat with an enclosure that small, and you can almost forget about airflow to the GPU.
I think the specs I listed above is about the bottom line if you want power and silence. Beyond that, I think you'll have to stick to Intel HD or something will overheat.
Even if you don't care about heat or noise, you'll also have to do the math trade-off with the PSU. Most small enclosures have PSUs that are lower than 300W.