Need help ??processors ?

The last one is the best. It has 6 megabytes of L2 cache, which is very important. L1 cache is usually up to 20 kilobytes because it's static RAM right on the die itself. These days, even L2 cache is often on the die so 6 MB of it will be very good. The L3 isn't listed but that is okay. A 1066 MHz front side bus will be good for communication with the hub's (chipset's) northbridge chip. This chip is used for communication with the RAM and video memory. So you will get fast communication between your AUTOcad programs and processor, which is very necessary. The southbridge chip is slower because the other busses connect to it but that's fine.