"as fast as the fastest PCs."
Pull the other one, it's got bells on!
Your mobile, low voltage components will be inherently less powerful, slower, & throttled as to keep the heat to a reasonable level, whereas a full desktop grade chipset will run at full power until either it or the fans seize up.
Your mobile chipset throttles back, downshifts, & plays "These boots were made for walkin'", my desktop upshifts, puts the peddle to the floor, & cranks up "I can't drive 55!" so it can sing along.