Actually The USS Constitution was one of 6 frigates designed by Humphrey. Constitution was one of the larger (heavy frigate) 44 gun vessels (not 42), along with USS United States (the first built) and USS President. Three other frigates were also built under the same act of congress (actually three acts to get them all built) all three of these were the "light" versions and 38 gun vessels. My the time Constitution made a name for herself, the "rate" system wasn't in common use any more. Vessels were referred to by their gun count. The heavy frigates would have been call 44's, but likely called "heavy 44's" for their power, speed and ability to absorb battle damage.
The heavy frigates typically carried 30 - 24 pounders on her gun deck in long guns, 20 to 26 - 32 pounders of carronade and a few of long gun 24's as chasers.
The differences are substantial, with the heavy frigate being 175 LWL and 2,200 ton, while the light frigates were ~140 LWL and 1,200 ton, literally half the size of their bigger sisters.
It's incorrect to assume The heavy colonial frigates weren't capable of firing broadsides, they were and did readily, though not nearly as often as the movies would have you suggest. In her engagement with HMS Guerriere, Conststution's first volley was a double load broadside, which surely would have "collapsed ship". Most skippers and gun crews had the good sense to fire as their guns came to bare, which was the logical route for accurate cannon fire. In this same engagement, Constitution repeated point blank broadsides, while the two ships were tangled after a collision. She earned her well deserved nick name after this battle. After over 2 hours of 25 yards or less broadsides, complete dismasting of Guerriere and it's surrender and subsequent sinking, Constitution was more than capable of continuing it's tour without returning to port.
What set apart the heavy colonial frigate was below her LWL. She was fine at both ends (not Cod's headed), which made her as quick as the much larger first raters, she would have to out run and considerably faster then the similarly classed vessels she'd do battle with. This advantage, plus unique construction made these heavy colonial frigates prized by all the world's navies of the era and out classed all of their rate.
When it comes to the "rate" of these heavy colonial frigates, it's difficult, as they weighed as much as a second rate, had the crew of a third rater, could out run a second and hold it own against a first rate and the armaments a high 3rd or low 4th rate.
This thread is getting old (4 months) and the original poster hasn't returned. I'll stick with my contentions in my first post on this thread (#5), in that no model making will help design even a fifth rater and considerable expertise is necessary, just like it was in Humphrey's day.