Remember, Pekkas don't target defenses, so your Pekkas could end up attacking in the wrong direction and get killed without dealing the most potential damage.  It could work, if you perfected your placement and maybe reconfigured your army.  I wouldn't suggest going without giants, though.  The best way to find out is to experiment on your own.

Pekka are also expensive! So the real question is: Is 1 Pekka better than 5 giants?  I personnally like the 5 giants. Pekka have a tendancy to circle the base. If thats the case your one powerful meat shield is marching in the wrong direction. Plus the giants attack defenses, which keep other units around longer.  I think a maxed pekka is a good suppliment. The space cost can be spread accross the various troops in your attack package.