27 inch iMac for editing and After Effects

Question

Hey everyone. I'm a student who does heavy video and After Effects work. Right now my core 2 duo macbook pro is not cutting it when it comes to performance and render times.
Luckily, my budget is around $2200-2300 thanks to money I should have leftover from my college fund (thank you, mom and dad).
I was looking at the MacBook Pro 15 inch until I discovered the 27 inch imacs that are in the library multimedia center. The screen size is great because there's so much space to work with and details come out a lot clearer.
But from a hardware and price perspective, the 27inch imac with a quad core 3.1 ghz intel core i7, 1 tb hdd, and a 2gb AMD Radeon HD 6970m is around $100 LESS than the MacBook Pro with a quad core 2.4 ghz, 750 gb 5400 rpm, and 1 gb 6770m.
The only tradeoff is portability, but given the difference in spec, i'm starting to say its worth it.
I know that a lot of AE is dependant on CPU and lots of RAM per CPU. Upgrading to 16 gb of ram is getting cheaper and cheaper (it also helps that the imac has 4 ram slots). The iMac can actually support 32 gb of ram, so when that becomes available that is another nice plus.
So just doing the math, with 16 gb of ram that would be a 3.1 ghz quad core intel i7 with 4 gb of ram per core. 8gb of ram when upgraded to 32 gb of memory.
I'm not sure what Apple is gonna do with the next iMac refresh, so I will probably wait until then to make a decision.
Does anyone have experience with AE on the 27 inch iMac with similar specs?
Many thanks,
Dan.

Answer 1

Several other drawbacks to the iMac or any other all-in-one computer system:
1) The GPU cannot be upgraded at all (at least not internally). In fact, iMacs cannot have their AMD (formerly ATi) GPUs disabled at all. And Premiere Pro CS5.x supports only NVIDIA CUDA GPUs for MPE GPU acceleration. (The current iMacs cannot be equipped at all with any GPU besides AMD/ATi.) Premiere Pro is thus forced to run in MPE software-only mode, which is much slower than with GPU acceleration.
2) No iMac has any room at all whatsoever for more than one single fast internal hard drive. Unfortunately, the interface that the iMac employs, SATA, is only a half-duplex interface (which means that data transfers can only move in one direction at a time). But video editing requires a disk system that does simultaneous reads and writes - but with only one disk connected only by a half-duplex connection, the system must wait for a given block of read operations to be completed before any writes of a given data can even begin at all. This slows down overall editing and encoding performance substantially.
3) Additional hard drives can be added externally - but the current external hard drive options available for the iMac are either very expensive or very slow. That's because the iMac has absolutely no USB 3.0 or eSATA capability whatsoever. The iMac has only USB 2.0 and Thunderbolt ports - but external Thunderbolt hard drives still cost nearly twice as much money per GB as other external hard drives, and USB 2.0 is limited in sequential transfers to only around 35 MB/s - far slower than the drives themselves are physically capable of (140 to 188 MB/s). Plus, of course, USB 2.0, like SATA, is only half duplex.