boris's original enb over at enbdev.com will add ambient occlusion, inject smaa, and add a host of other dx10 effects like water caustics and volumetric shading. the enb also does hbao much better performance and quality wise than nvidia forced settings. so you do not need an nvidia card at all to enjoy "dx10 like' skyrim, amd cards handle it very well. also the memory management built into the enb can cut vram load down almost in half in some cases, especially with heavy mods.
maxing out vanilla skyrim@1080p using the stock enb enabling smaa and af doesn't require much horsepower at all, say an fx6300/i5 quad and a hd7870/gtx660. running a full s.t.e.p. highest possible quality mod install@1440p will require an overclocked amd fx 8 core or overclocked intel 4 core and an r9-290 or gtx780.