Hi MagicThief83,
Let me start by saying that I fully understand your comments of both not wanting to buy a windows-only machine and of wanting to buy the Retina MBP -- this is understandable to me.
But let me say that if you already have a Thunderbolt external drive, such as a RAID with striping or perhaps even a fast SSD, then you should be able to store both your games as well as your multimedia on the external drive with little or no compromises to your playing/viewing experiences. I would not worry about storing your games/multimedia on an external drive being "too taxing on the drive and increase the risk of HD failure" to quote you, as these drives are designed to handle this type of usage. And if you are still worried about this then I would recommend that you purchase enterprise-class HDDs, which have a longer warranty and thus presumably better quality control, instead of consumer-grade drives. This is especially true if your HDDs are in any type of RAID system, as the enterprise-class drives do ERC (Error Recovery Control) which means that they "wait" before actually reporting disk errors to see if they are single sector errors and thus can be eliminating by remapping to an unused sector. In other words, having a consumer-grade HDD in a RAID can be problematic since these drives will typically immediately report read/write errors to the RAID controller which then might immediately mark the error reporting drive as "failed" and remove it from the pool of RAID drives forcing a time-consuming repartitioning of the data across the remaining good RAID drives.
[Let me briefly describe a similar resource-taxing usage of external storage and the rMBP. Now I don't personally play games on the rMBP, but I do perform some heavy number crunching that fully taxes the CPUs of the rMBP along with 3D visualization that is capable of taxing the GPU also. (The rMBP is actually only one component of several performing these computations - the latest one to be added.) The data sets for this work are quite large and sit on external RAIDs (SAN), being transferred over Thunderbolt to the rMBP's SSD or over Fibre Channel to other servers when needed. So far the rMBP is more of a visualization tool, really "toy" might be more appropriate, to this project because of its portable high resolution display, but I foresee rMBPs becoming more integrated and more important to this work. The take-home lesson is that transferring data to the rMBP's SSD when needed over Thunderbolt is a viable option.]
Lastly, allow me a further suggestion. Since high capacity external HDDs are fairly cheap today (okay, so before the Thai floods they were even cheaper), I would recommend that you get a separate external drive, say a 3 or 4TB one with USB3.0 interface, to backup your rMBP and your current external 1TB Thunderbolt-enabled drive that you store your games/multimedia on. This third drive only serves as your backup. It does not need the communication speeds of Thunderbolt since only the initial backup, whether by Time Machine or Carbon Copy Cloner, will be large with all subsequent backups being much smaller. And USB 3.0 is plenty fast for this. In fact, you might even think about a 3TB Time Capsule and perform your Time Machine backups wirelessly to the Time Capsule. (After the initial TM backup, wireless will be plenty fast for your subsequent hourly TM backups.)
In summary, your Thunderbolt-connected 1TB HDD (or RAID?) should store all of your games/multimedia and give you fast enough communications to your rMBP so as not to adversely affect your playing/viewing/listening experiences. A cheap third 2/3/4 TB external HDD with USB 3.0 interface then serves as your backup drive. You then won't need to spend an extra $500 on the Apple 768GB SSD for the rMBP, this savings then more than pays for the third 4TB USB3.0 backup drive. If you find that one particular game suffers from being played over Thunderbolt on your external 1TB drive, then you can always transfer this game to the rMBP's SSD whenever you wish to play it. What do you think? Sound like a viable solution to you?
Regards and have fun with whatever system you eventually settle on,
Switon