How to fix resolution problem in Photoshop CC for Macbook Pro w/ Retina Display

Question

I design email promotions for my website in Photoshop CC on a new Macbook w/ retina screen. However, document sizes appear much smaller in my Macbook than they did on my windows laptop. A 700px wide document now appears to be 350px wide.
When I designed the email graphics, upload, and then view in a browser, everything is pixelated. The document/graphic is still 700px, but its pixelated in the browser. After some Googling, I have a better understanding of the problem but not a complete understanding. Its all so technical. I've read that some designers choose to create their graphics with another lower resolution monitor connected to their Macbook (if I explained that correctly)... not an option for me, though, unfortunately.
How can I fix this problem? I basically design for the web so its important that these graphics are at their highest resolution when viewed on a web browser. Any solutions? Help! I will try everything in my power. 

Answer 1

First of all, thank you so much for taking the time to try to help out. It
is much appreciated.
The two things that first come to mind are: I have many friends in the
industry who paint solely in Photoshop and do just fine. My computer is
technically "old," but the specs are still just fine—even the graphics card
is the exact same one that is in the new Cintiq Companions (the all-in-one
computer/cintiq machines).
And, more so, I was painting on it for a few weeks without noticing
anything. A part of me wonders, did I just not notice it until it became
dramatically worse?
I do remember painting fur, which requires making tons of small brush
strokes over an extended period of time, and I don't remember there being
any lag.
By the way, I forgot to mention: I've even tried going into the Performance
preferences and disabling the graphics card altogether. No luck. Still an
issue.
As far as painting at 100%: I do notice an amount of improvement. The one
brush stamp, or space, whatever you call it, issue only happened on the
first brush stroke (every time) and then just once otherwise. The lag was
tremendous—and I compared it to Painter's performance, which had no issues
whatsoever.
I am really hoping to be able to rely on Photoshop more and more, as its
tools for other aspects of image manipulation are far more robust than
Painter's. And the working compatibility with Adobe InDesign, Flash, and
Adobe Media Encoder are sooooooo useful for speeding up the workflow.
Hopefully we can find out what's going wrong.
I'm truly baffled on this one.
Bryan Beus
Artist and Author
www.bryanbeus.com
Sent from my Tardis