Not to be argumentative ... but ... Sorry Max. They ARE sharp and show NO pixelization - even from a couple of feet away.
You're welcome to come by my studio and check them out any time you're in Northwest Florida. Several serious, and very picky, professional photographers around here have seen them. So it's not just me saying this.
I'm sure it has a lot to do with the quality of the original (excellent!), the ability to do post processing the right way (yeah, I really DO know how), and the quality of the printer (in this case, an Epson 9600 in the capable hands of one of the most experienced printers I've ever worked with.)
Sadly, there will always be some who'll say it can't be done ... while others will just go ahead and do it.
NOW! Back to ChrisF79 ... Go for it! Maybe work up to these sizes, but don't be afraid to try. And, more important! While you're decorating your apartment, you could do worse than to include a couple of great pix of that girlfriend of yours.