This is not right:
big cog in the front = you go faster, for the same pedaling speed.
big cog in the back = you go slower, for the same pedaling speed.
So the 42/13 in the example is a pretty hard gear. You'll go 14 mph at just 60 pedal revs per minute, with this gear on a mountain bike.
I guess my post wasn't clear somehow, because that's exactly what I was trying to say. (As someone who explicitly put a 22/34 on my touring bike to be able to ascend 12% grades with a 50lb. load, I definitely understand how bicycle gearing works!)
The OP had already said that he was in his "hardest" gear. Someone suggested that gear was not "hard" enough for him, and thus, he needed a crank with a bigger front gear. I was disputing this notion, by illustrating that even with the "least-hard hardest gear" I could imagine on a bike, it was still a plenty-hard gear; all he needed to do is up his cadence. And yes, I used Sheldon Brown's gear calculator to come up with the 21.5mph he'd be going at 90rpm, which is plenty fast for anyone, which told me the OP wasn't riding with anything near a 90rpm cadence.
This isn't the first time someone here has asked if their gearing is wrong. It's never the gearing that's the limiting factor. It's always the rider. If someone actually has the ability to push the bike at 35mph and genuinely needs higher gearing, they aren't asking about it here, since they're already on a pro cycling team.
Thanks folks... i feel kinda dumb now but my bike isn't too slow given that on my commute back yesterday and my rpms. I was so tired by the time i got home (in record time) and my pedaling still wasn't as fast as people here are saying... now my legs are jello and sore :(
but the good news is i have lots of "bike" left to max out speed
No reason to feel dumb; as HenryDavid astutely said, you were probably just doing what felt "normal" to you. Whenever I see slow-pedalers mashing on the pedals, I always want to let them know that they could greatly improve their experience by pedaling faster in a lower gear, but there's pretty much no way to say that while riding by without coming off like an asshole.
Now you know how much more your bike can whip your body into shape; take it easy for a couple days to let your legs recover, but then go back to that effort level. But shifting to a lower gear will allow your pedaling to go faster and be more efficient. In a month's time your commute will feel as easy as it did two days ago, but be way faster!