ok, i just did some tests and i was half right and half wrong.

x=x<<4+x<<3+x was quicker (taking 80% of the time that x=x*25 took to execute)

However, what surprised me was that x=x*25 used MORE code space than x=x<<4+x<<3+x. Replacing x=x<<4+x<<3+x with x=x*25 in my program adds 338 bytes.

It appears that x=x<<4+x<<3+x wins on both counts.