Unfortunately those websites are built using html5, not flash.
Previous iMacs and Macbooks with lower resolutions handle those sites fine, thats why I'm disappointed with Apple for building machines with high resolution displays and not-so-good graphics cards backing them up.
They run very well at 60fps on my Macbook Air and Windows machine :/
This Flash tester site indicates they are using Flash. I realize this is not conclusive. Note the free version of this site will only test a web site every 30 min: http://seositecheckup.com/tools/flash-test
You are making conclusions that are not supported by your testing. There are too many factors in play. I tried one of the awwwards websites and it was clearly a buffering issue that was causing it to stutter. It is true the 395X isn't as powerful as many desktop cards (but the iMac is not a desktop machine, it is an all in one) and it is not as powerful as some of the latest mobile GPUs from Nvidia. But to come to the conclusion that it is underpowered for the 5K iMac based on some website difficulties is logical fallacy. For those of us working with the most demanding graphics possible (4K video and RAW footage) we do not find the graphics card underpowered. Myriad professional reviewers have come to the same conclusion.
Well Floris, what will you be doing on the machine?There is a 14 day return period. And everyone else on the thread who is using the computer regularly for demanding tasks has told you the choppy graphics are on the occasional website are not a hardware issue. Let us know what you are planning to do with the computer and we can better advise. Also, the rMBP has less video graphics power
lots of illustrator and photoshop, web dev, web design, photography, vlc+media for tv/video, vlogging on premiere pro, games like minecraft once in a while, and big 4gb+ mysql database stuff, writing.
There's no need to use external sites to check how those sites are made, if you have programming experience just check the code, elements, network or js profile on the developer tools. Maybe that site reports flash usage because of the sound library, wich sometimes uses flash audio as a last resort if html5 audio isn't available. You can see the animated elements on the developer tools very clearly and they're html5 with transforms applied by css and javascript.
I don't have right now an iPad to test it on, but on my iPhone for example one of the pages shows a message like "this site has no mobile verion, please use a computer or tablet". Because of the multitude of devices, developers of heavy front-end websites usually choose to serve different versions each one adapted to the device is viewed on (or browser, OS...). There's nothing wrong with seeing different content on different devices.
Yes, it can be caused by a software issue. Or by a hardware issue. Or probably both I believe (poor graphics card on a 5k display and lack of browser/os optimization). The thing is I need a computer to work, one that shows websites at least at the same framerate as my Macbook Air. I think I'm not asking for too much considering it's a 4.000€ computer.
As he said you have 14 days to try it. I'm not trying to bash the new iMac with my posts, just letting everyone know my experience with it.
All of them have won recently some of the most important awards in web design. There's even an art director from Apple as a jury of those awards.
Right now, the adobe creative suite and El Capitan are not playing nicely. Although I am using Premiere to edit a 4K piece, there are some graphical bugs. It is all software and Adobe and Apple are working on fixes (Apple's most recent update fixed some of the most egregious problems with premiere and Adobe has said they are working on fixes). This is typical when Apple rolls out a new OS and Adobe software is never bug free. You aren't supposed to update the OS until Adobe says it's okay -- but with the new 5K Skylake iMac, you have no choice but to use El Cap. We'll see fixes within a few weeks. That said, the websites above played fine for me.
It's an attractive design but ultimately it must work efficiently on the broadest possible selection of devices. You can win all kinds of design awards (from other designers) yet have a product which doesn't play well in the real world. For recent expert commentary on this, see: http://www.fastcodesign.com/3053406/how-apple-is-giving-design-a-bad-name
The problem is you initially said it was a clear-cut GPU deficiency. We are only pointing out it is not so clear cut.
The 395(x) is just a 295(x) basically, .. ATI is known for that misleading renumbering.
If it's only a rebadged 295X, how did the 395X managed to produce better performance in these tests: http://barefeats.com/imac5k13.html
Not saying they didn't use newer stuff.. but perhaps look at this too; http://videocardz.com/55499/amds-hawaii-gpu-to-return-with-radeon-300-series
