I did a setup similar to Gert"s on a 6.2 (I7 Quad), same SSD 512GB M4, but I added Crucial's 16GB ram. It absolutely flies. For Francesco De Giorgio, you need to boot off the Mountain Loin that shipped, don't ask me why, but normal OS X downloads aren't working for these upgrades (you see it all over the inter web right now), something is unique, the what shipped, which leaves cloning the original drive as the best option at the moment.
I found this as well when I added my SSD today. My tape/plastic piece bent out of the way just fine, I was uber careful and held the antennae connector down while I pulled the tape up so as to not pull the connector off at an angle and damage it. WIFI and SSD work just fine still for me after reassembly. My guesses for what it is are... 1. A piece of tape that one worker on one of the many lines put in the wrong place (maybe didn't cause a QA concern so they left it, would explain why not everyone has seen it) 2. retaining tape added during assembly diagnostics (for connectors deemed loose) 3. A tamper seal of some sort, but I would think everyone would be seeing it. Just my thoughts, but I'm a MechE and may be over thinking it.
It depends on what you need, Intel 4000 is integrated, and uses system RAM to operate. Upgrading to ram increases the ram dedicates to video, for example I'm running 16GB on my 6.2 and that bumped the VRAM to 768MB, the OS may be able to Modulate this up to the intel limit (2Gb I think I read somewhere, but don't quote me) But I haven't seen it yet. Keep in mind this will always be DDR3, which is slower than a dedicated card. If DDR3 isn't fast enough for you, Thunderbolt may someday be your solution.