RE: Studio XPS 435MT ... a new life with win8 and GTX 650 1GB DDR5
I didn't change my case .... used the stock case and P/S, then replaced the stock video card with the ASUS GeForce GTX 650 1GB DDR5 PCI-E Video Card. Its still going strong 3.5 years later.
Whatever case you get just make sure you get good quality P/S to go with it .... I would say 500w absolute minimum..... would be better with 600-700w. The standard 360w that came with my system was maxing out after just adding a second HD ( and with its original video board). Only my swapping in the low power gtx 650 video card did i gain enough power headroom to keep it working.
As the P/S gets older their output starts to fall off .... but maybe you already have a new P/S ??