$2K absolute max for a new Mac

My white iMac (1st gen Intel) is just not cutting it and the wife has OK'd a $1500 upgrade.  I have a camera fund (we all do right?) that currently sits at $500 and though I'm dying to get a new camera, I really don't want to end up with a mediocre computer.

My current iMac has 3GB Ram (don't ask), 2.16 Core 2 Duo processor, ATI Radeon X1600 128 MB, with 256GB HDD and a 1TB WD USB 2.0 external HDD.  I've had it for around 7 years. As of late, I find simple tasks in LR and PS to be painfully slow.  My files/catalogs are extremely unorganized because I just don't want to deal with the how long it takes.  I've been into photography for just over a year (but used PS for quite some time now for graphics/design) and any type of photo editing is just dreadfully slow.  I've been getting into video editing lately and want to do more, but my computer practically refuses to let me edit videos so I've stuck to stills for the time being.

Now, with that being said.  I do play some games on occasion (RPG, FPS, and RTS) but it's not my priority to have an optimum system for gaming, just one that's do-able.  My current computer can't keep up with fast FPS games or if there's too much action in a certain scene.  My main priority is to be able to use Adobe products.  Though I do not know too much about video editing at the moment, I am planning on getting into it and I would assume I'm going to continue using Adobe as well.  LR4 is my number one used app with photoshop and a bunch of plug-ins (Nik, Photomatix, Topaz, etc).

I am somewhat technically savvy, but one thing I do not understand is Video cards.  I understand that bad ones make hardcore games crash and good ones make them run smooth.  That's about it.  I really don't want to get into the 27" iMac due to price, but the 21.5" doesn't offer an upgrade option to the NVIDIA GeForce GT 650M 512MB GDDR5.  I can max out the RAM at 16GB, get a 1TB Fusion drive and the i7 processor but I'm stuck with that video card.  Is this going to be enough for the things I want to do? I know a better video card would help out with games (which I barely care about), but does it make a difference in any type of photo or video editing or graphic designs (ie: Illustrator)?

My other option is to get the 27" iMac with...

• 3.4GHz Quad-core Intel Core i7, Turbo Boost up to 3.9GHz
• 8GB 1600MHz DDR3 SDRAM - 2x4GB
• 1TB Serial ATA Drive @ 7200 rpm
• NVIDIA GeForce GTX 675MX 1GB GDDR5

I hear that the Fusion drive is awesome and I'd be missing out on that by going with this option but at least it's a 7200rpm HDD.  I can always upgrade the RAM later.

I've been sticking to the i7 options simply because I've read that the processor means more than anything else as far as speed goes in Photoshop.  Am I putting too much emphasis on this?

Any help would be much appreciated... again, I have $2k MAX.  Oh, and I also get a student/faculty discount via my amazing wife.