Had the opposite experience. My first Apple computer, a 27” iMac lasted less than 6 months on my desk. Gave it to my daughter, and bought a more robust Windows machine for less money. The horsepower just wasn’t there. It had a criminally under powered video subsystem in a $3k machine, and I had upgraded to the best available. Now I have a machine that can actually run my software at native 2560 by 1440 with acceptable frame rates. The more expensive iMac could not, and that’s a bottom line you just can’t cheat.
Where to start ...
If your iMac died - take it to Apple and walk out of the store with another one. Apple is probably one of the top end stores in the Customer Support arena
$3,000? Really? iMacs in the 27 inch range start at $2,000. Upgrading to a 2 Gig AMD HD6970M takes you to $2,299 (including the upgraded i9 Intel Chipset). It would be foolish to buy the additional memory from Apple, as they are 2-3x more expensive for the same DIMMs from Amazon.
At the $3,000 pricetag, you would want/need to hit the Mac Pro with the Xeon Processor, 16 GB RAM, 1 TB Hard drive and then run two of the AMD HD5770's each with 1 GB of RAM. That would set you back to $2,749. You can get a very good Dell Ultrasharp 27 inch monitor in the $250 price range.
And, if this isn't enough - you can bump from the 4 Core Xeon processor, to the 6 Core Xeon.
I think you will admit that is a pretty powerful workhorse.
Apple or anyone else - pretty much everyone in this league uses the same Intel chipsets.