The books are not exactly the same. The 5000 recipe version is a new edition of the "Guide," translated and published in England about fifty years ago, with some subsequent editing and with metric measurements (I'm not sure about the original English edition).
The smaller one is put together from a few sources, including the "Guide," and updated in the senses that the work was done more recently (2000 ish), and the recipes were tested and adapted for American measurements.
Most of us would find the smaller book easier to follow. Setting that aside... Is bigger better? Hard to say. Either one will introduce you to the same pre WWI culinary thought, techniques, and classic dishes. I wouldn't choose one over the other because one included a more comprehensive collection of recipes which were already passe 75 years ago.
There's also an illustrated version of the Cracknell translation with less than 500 recipes.
Personally, I prefer Pellaprat.
BDL
Edited by boar_d_laze - 9/7/12 at 7:19am