You're planning on carrying around a device larger than the laptop? No, I didn't think so.
I amazes me how many people just don't understand what the TB port is. The TB port is a 4-lane PCIe path, at best. Graphics cards are 16 lane. So unless you are planning on only utilizing 25% of the bandwidth, this is a failure. This is also why a Retina external monitor is likely going to come with stickers "for direct connection to the computer only" Go take a look at benchmarks where the benchmark user saturates the TB bus and has the monitor running at maximum resolution.
The TB port, as-is, is not in a state where you're going to be able to just dump anything on it and get 100% of the performance. Adding a retina display goes from 5.8Gbit/sec at 1920x1200 to 21.4Gbit/sec at 3840x2160. Display port supports only 17Gbit/sec of video bandwidth. The TB interface only supports 40Gbits of half duplex communications. So where are you going to get the bandwidth to run a video card when it can't even push the pixels required for the retina display?
The reason for Safari's performance to be pretty poor on a high resolution display, lies in the underlying way web browsers render things. They are not natively using the video card at all. All of it is done on the CPU. Things like Adobe flash, even when they are GPU aware don't even scale beyond 720p because of limitations of the flash platform. Go take any old flash cartoon made with Flash 8 or earlier, newgrounds has plenty of them, maximize the flash animation. You'll see several issues:
1. If it contains flash video, it will tear into "bands" across the number of cpu cores in the system
2. If it contains vector animation, it will drop frames at all quality levels once it gets past 720p. Expanding it to 1080p or the Retina display will likely see it drop into single-digit framerates. This is because Flash, is only as fast as a single core in the system, which we've gone from 3Ghz cores in the Pentium 4 down to 1.7Ghz cores in Ivy Bridge.
As a result, Webkit is also only as fast as a single core in the system. You may get separate threads working on different tabs, or separate threads working on separate flash animations in the page, but ultimately, only one thread is ever used to render a web page. Even Javascript implementations in other browsers have gone from supporting multiple threads to only a
single thread , so the reason facebook gets slower with the larger the screen real estate, comes back to only one thread being used for a script. Little of the page can be rendered directly on the GPU since it has to interact with the web browser DOM anyway.
So you're seeing the slow down because more has to be done by the CPU. Not the GPU. 4 cores don't render a page, only one does. When you make that page 4 times larger in area, you don't magically get that for free.
