Damn you Scout dad. Posted while I was joting this one down...
The F5 in SFB was the Proverbial Wolf in Sheep Clothing. She could do it all. The F5 Size, Weapon Suite, and Power Systems made it easily a match for any Frigate in the game and also for most Destroyers and War Destroyers through the early part of the General War. When the F5C came along things only got better.
Unfortunately when the F5 was translated into FedCom it was it size that did it in. When the Move Cost was being calculated its Fractional Movement Cost was rounded up to make it fit in to the way Fed Com calculate movement and by doing this the F5 actually started paying a Movement Penalty per se. The Federation Frigate has a Total power of 18 but with its ¼ move cost it only takes 33% of its available Power to move Speed 24 where as the F5 with its 21 Total Power and a Move Cost of ½ would pay 57% of its Power to make the same Speed. This resulted in the Fed FF actually gaining a little in its combat potential where the F5 actually lost a little of its Combat Prowess. The flip side to this is the Klingon E4 which despite being called an Escort really was the over looked Frigate of the Klingon Empire. With the changes made bring it into FedCom it now actually has a good chance at standing Toe to Toe with its larger Cousin.
So in the end a bigger size does not translate into a better ship. You have to look at all the Pieces to see how they fit together.