I'll note that any comparisons I make will be to the parts that ETKA says are correct for a GLI. Older parts may actually work just fine - I suspect that if you walk up to a 2005.5 Jetta, drop the rear suspension out of it all intact, and then lift it straight up into a 2011 Jetta, it'll work adequately.
http://bhtooefr.ath.cx/files/ETKA-2011-JEM-IRS-Rear-Axle-Beam.pdf
This is the central rear beam. ETKA shows that it's also used on late 2006 and newer Mk5 Jettas, including wagons. Something to watch for is that 4 of the bolts are different between PQ35 cars and the Jetta - the bolt numbered 3 on this PDF. However, dimensions are the same, it could be a production revision.
http://bhtooefr.ath.cx/files/ETKA-2011-JEM-IRS-Control-Arms.pdf
Here's the actual suspension components that bolt to the rear beam.
So, a list of what to watch for, here:
#13, Track control arm, rear upper: 2009+ cars only, it looks like.
#16, Wheel bearing housing: This is Mk6 GLI specific, it looks like. A Mk5 part may work, but you run the risk of causing other problems, there.
#18, Bolt, hex. hd. (combi.), M14x1.5x115: This is normally used on 4Motion cars. The same part on Mk5 FWD cars is only 95 mm long. I'd guess that the wheel bearing housing mandates this, based on the ETKA diagram.
http://bhtooefr.ath.cx/files/ETKA-2011-JEM-Shocks-Springs.pdf
And here's shocks and springs. This is mainly component selection, you may want to mix and match in the parts bin or with the aftermarket to pick what suits your car the best, although there's a few different parts listed... keep in mind that the Mk6 cars are about 100 pounds LIGHTER than the Mk5 cars, IIRC, when doing your suspension tuning. (Then again, the IRS might add some weight back in.)
#16, Rivetted cap nut, M6/0.5-3: This is a 2009+ Passat CC, 2010+ Golf, and 2011+ Jetta component. Weird. It's an NLA part on older cars, and I think may be part of the lower control arm? Not sure.
#17, Stone guard: This is also NLA on the older cars. Maybe it's not actually available for them, and the cap nut attaches it?
#18, Bolt, hex. hd. (combi.), M6x12: Same deal.
#19, Rivet, 8mm: Ditto.