Several people have mentioned that they were getting good performance with similar machines. Try looking at the threads in the "More Like This" box to the right and searching on "macbook pro". There are also a number of threads discussing UI problems with the retina display. You might try searcing on "retina" as well.
I am currently running SW on a 2013 MacBook Pro 15 Retina. I upgraded from a Beast of a Dell Precision M-series. I say upgraded because Apple is much lighter, not to mention battery ife is crazy awesome.
I am running Win7 Pro 64-bit and have had zero issues with crashing or lag. I admit I run very few FEA's, but when I do, the parts are really BIG parts, not many, just BIG. I have my system kooked up to an Apple 30-in Cinema Display @ 2560x1600 (can you you say View-mongous) with zero display issues. Sometime when I print a PDF of an assembly, it will crash. But I believe that to be compatibility issues with software.
I would say that Win 8.1 is too new and still glitchy. And I would add you lack enough hardware HP to run SW. I run ACAD2012 simultaneously with Outlook and watch Netflix all in the same session, swap back over to SW and keep on trucking.
thx for taking the time to get back to me. i think it is down to hardware so i will have to use my uni computers until i can sort an upgrade.