Well, the size of the legends for the alphas is sort of immaterial since they won't match ordinary SA alpha legend size no matter how big you make them. This simply due to the fact that you have to make room for the APL secondary legends.
7bit re-did nearly all the legends for Round 6 Space Cadet, and they are a tiny bit "bolder" than SP's standard legends for SA. You can mix and match them with keys from other sets but you will notice a small difference in the line weight of the legends. And, of course, the F-row keys all have bigger legends than normal, which makes them more readable I suppose, but also makes them difficult to match up with keycaps from other SA sets.