Daniel,
The first thing to consider is what aspect of your system would provide the greatest benefit for it's use. If you are doing calaculation-intensive work, it may be the CPU and/or the drives, but for visualization applications, it may be more more useful to concentrate on the GPU. The system already has the maximum32GB RAM and changing from 1333 to 1600 will not be noticeable (the faster the RAM clock speed, the higher the latency).
CPU: Staying with Xeon's, here is a handy shopping list for Xeon E3-1200 v2's (LGA1155):
http://ark.intel.com/products/series/75142/Intel-Xeon-Processor-E3-1200-v2-Product-Family#@Server
The E3-1245 is a good performer already. The average Passmark CPU mark is 8075 and with a single thread mark of 1882. As you are doing 3D CAD, having a higher single-thread perofrmance is going to be noticeble, but it should be farily good jump to make it worthwhile. Comparing versions of the E3-1245, the E5-1245 v2 has an average mark of 9074 and single thread of 1992 and the v5 numbers are 10303 and 2157. The Xeon E3-1200 v2 with the highest single-thread rating is the E3-1280 v2, (4-core @ 3.6 /4.0GHz) with an average CPU score of 9758 and single thread of 2139. For Unreal engine 4, that would be my suggestion.
So , in considering CPU replacement, look at the list of E3-1200 v2's and consult the Passmark CPU Benchmark page to compare performance and then choose by need and price- cost /performance.
GPU: Upgrading the Quadro 3000M is probably going to provide the most improvment. In Passmark baselines the average 3D mark of the 288 samples tested is 1329. For your use, in my view, the 3D mark should be say, 2800 or better. Unreal Engine recommended hardware focusses completely on NVIDIA GTX and I would say, in general, consult the Passmark Videocard Benchmarks page and buy the GTX with the best performance within your budget.
Cheers,
BambiBoomZ
HP z420 (2015) > Xeon E5-1660 v2 (6-core @ 3.7 / 4.0GHz) / 32GB DDR3 -1866 ECC RAM / Quadro K4200 (4GB) / Samsung SM951 M.2 256GB AHCI + Intel 730 480GB (9SSDSC2BP480G4R5) + Western Digital Black WD1003FZEX 1TB> M-Audio 192 sound card > 600W PSU> > Windows 7 Professional 64-bit > Logitech z2300 speakers > 2X Dell Ultrasharp U2715H (2560 X 1440)>
[ Passmark Rating = 5581 > CPU= 14046 / 2D= 838 / 3D= 4694 / Mem= 2777 / Disk= 11559] [6.12.16]