Hi Himmet,
I fully agree with Sascha. Our experience have shown, that e.g. the ARM Cortex M3 is able to sample data up to 1kHz. However, if you want to move into the 2 or even 3 digit KHz range, the blackfin is a good choice. We have achieved block oriented data acquisition at 250kHz and continuos daq at 50kHz.
The issue is not primarely to sample the data. This might be achieved by the underlaying low-level drivers written directly in "C". But the data needs to be processed (floating point !) , saved to a filesystem, communicated somewhere. There's where we have found most of the bottlenecks. Algorithm-benchmarking is a good means to find them.
Best regards
Marco