The other thread has the majority of the GPU discussion, including benchmarks from mtrlt, the developer of Reaper (the first GPU kernel released for Litecoin in response to ArtForz's claim Litecoin was GPU resistant).  I disagree with ArtForz's claim that increasing N helps GPU's once both CPU's and GPU's are computing hashes large enough that they're pushed to external RAM.  I would say ArtForz's analysis was cherry-picked based on the specific value of N (8192) where computation gets pushed out of the L2 cache on the AMD Phenom II he was testing with.

Indications, including from mtrlt's benchmarks, are that the performance spread between CPU's and GPU's narrows as N rises.  As long as we don't cherry-pick a specific result from a certain value of N on an AMD Phenom II CPU..

Also note that YACoin doesn't use the same scrypt variant as Litecoin.  The mixing algorithm is switched from salsa20/8 to chacha20/8, and the hashing algorithm is switched from SHA-256 to Keccak-512.  Direct comparisons between hash rates of the two aren't quite going to be an apples-vs-oranges comparison for a given value of N.