Completely correct, any speed difference you notice is either due to performance factors on the two machines (not to do with the wireless speed) or just psychological because you *know* one is only working at half connection.
I do have a theory as to what's causing it. My guess is that the 75Mbs connection speed is the *actual* speed for both laptops. In practice I've never really seen any speeds above this, so I reckon this is what both your machines are operating at. The difference is probably in the wireless drivers, one is most likely reporting the actual connection speed and one is most likely reporting the theoretical maximum (yes, with a lot of hardware this is 150 rather than 300 as commonly believed.) So if you're after solving the problem to see the actual connection speed then you'll be wanting to put the 150 one down, not the 75 one up
As said above, nothing to worry about, it's perfectly normal. If you really need that much bandwidth (and I really doubt you do) you shouldn't be running over wireless at all - gigabit ethernet is around for a reason!
