Please help.... iMac or iMac Retina 5k?

I could sure use some basic guidance and suggestions here...

First concern:

Money isn't really the issue, and I know the 5K is insanely better display-wise but my hang-up is that the Retina might be TOO good.... Example: I hopped on one of the 5k displays at Best Buy and browsed around at some of the websites I've recently designed only to realize how crisp some of my UI elements WERE NOT.... I mean... A 5k monitor is as good as it gets but it seems like total over-kill for web-design... How would I ever make 72 dpi elements appear CRISP on a 5k display?

My second concern:

SPEED is why I'm looking to upgrade..... Would I be sacrificing performance if going the 5k route?

Thanks!

It sounds like you've pretty much already figured out your question, and there are also a lot of articles with the question and answer with a google search:
https://www.google.ca/search?client...&oe=UTF-8&gfe_rd=cr&ei=10mXVcTvKITt8weW6Z2wBQ

and resulting hits like:
iMac Buyer's Guide: Is the 5K iMac Right For You? - Mac Rumors
and
http://gizmodo.com/imac-with-retina-5k-display-review-do-those-extra-pixe-1652463922
etc. ...

tommytime555 said:

Example: I hopped on one of the 5k displays at Best Buy and browsed around at some of the websites I've recently designed only to realize how crisp some of my UI elements WERE NOT....

Click to expand...

High DPI displays are the future. If your existing work doesn't look good on these displays, then don't you think you SHOULD get one to make sure your work does look good on them going forward?

Even when money was tight, I went for the 5k display. It was a no brainer decision.