First question, does that laptop have a SSD? Most developer machines do these days, that's the single biggest improvement to build times you can make. Then look at CPU, IO, memory utilization during builds to see where improvements can be had.

Generally speaking... "productivity" and media styles of workloads do better with more cores/high memory machines. Gaming typically does better with higher clock speeds (which means less cores in every case I've seen). If you want that in a laptop form factor though, I am not aware of Intel sticking massive-cored chips in the mobile form factor, so your choices will be limited to whatever the fastest i7 is you can pickup... unless you were thinking of building a desktop?

UPDATE - Oh mutagen's point about SSD is absolutely spot on... the faster the storage the better _first_... then worry about the rest of that stuff I mentioned.