Modern microprocessors are loaded with a lot of performance optimization features. Single Instruction Multiple Data (SIMD) instruction set feature specially designed for improving the performance of multimedia applications is one among them. But most of the encryption algorithms do not use these features to its fullest. This paper discusses various optimization principles to be followed by encryption algorithm designers to exploit the features of underlying processor to the maximum. It also analyses the performance of four eSTREAM finalist stream ciphers – HC-128, Rabbit, Salsa 20/12 and Sosemanuk – under various methods of implementation. Scope of implementing these stream ciphers using SIMD instructions is examined and improvement in performance achieved by this implementation has been measured. Modifications in the algorithm which provide further improvement in performance of these ciphers are also studied.