I've used 3ds max for a few years, and personal experience has taught me render performance is independant from your video card, but relies solely on the processor. The video card does effect your fps in the view ports and their performance, but didn't do anything for my render speed. Personally I would drop $100 off your gpu purchase, and add it to cpu to get a Phenom II X6.
For a maya only setup, you don't require to invest heavily on the display card unless and until you are working with huge textures and data in the scene in which case also, the 5850 will be useless.. For those scenarios you need to pick up on a workstation class card (quadro fx 1800 a viable solution).. Now if you are looking for good render times then the most and the only important part is the CPU.. You can do better than your current CPU selection by going for a less costly card and a more powerful CPU.. I'd suggest you go for something like a Nvidia GTS 250 1GB.. 4GB is a good initial start for RAM but eventually you'd do better with 8GB.. Get hold of a phenom II X6 if you can..
1-Will Directx 11 support have a significant effect on maya? (even in the next 2-3 yrs)
2-Is the current graphics card better, equal or worse than 5770? (CUDA support,....)
3-Is the processing power enough or is the phenomII x6 worth the wait?(still not available in my country)
Finally, any recommendations, advice is MOST welcome & appreciated (and SERIOUSLY needed).Please note that this case won't be upgraded for about 2-3 years.
I'd have actually suggested the GTX 260 had you not mentioned the 5850 in your query which made me think that you want dx11 also.. DX11 will stay irrelevant for some time more to come.. Actually, i believe directx is more required for max than maya.. The performance numbers can be compared only in games wherein the GTX 260 performs on par if not better than a 5770.. Just be sure to take the one with 216 cores.. To answer your third query, more cores are always better when it comes to render calculations and i'd really encourage you to go for the 6 core as It'll help to stay away from any required upgrade needs for a long time..
Autodesk haven't even got DX10 support right yet (especially if you want to use the infamous viewcube and other widget-like things in the viewports), so I doubt DX11 is on their agenda. I still use DX9. If what you waste most of your time doing is the final render then you'll want a powerful CPU. You'll either want to look at a Core i7 system or a Phenom II X6. An X6 1055T is only marginally more expensive than the X4 965, while the 1090T is over $100 more. If you can, overclock the 1050T to 3.2GHz and you'll have yourself a 1090T for alot less money (you could try and go higher but that's up to you) A 1090T or equally clocked 1055T will be ahead of any stock clocked Core i7 except the 975 and 980X, but will probably fall behind those other chips when they are moderately overclocked. But they are also more expensive to start with.