Yeah; if you get 45F out of vent that's damn good. You sure could get a bit more CFM out of there and maybe rustle your arm hairs; but perhaps not with these beefy fans. I'm going to take a fork from Reload's topic and suggest that there's something mechanically wrong here and may be hard to find without ripping the dash out (I even cringe at that!). 300CFM is fairly typical for a squirrel cage and should be enough for 4 registers.
Let me set up a recent example I found in our home and see if you still follow for the problem I had in mind: Heat kicked butt the first "Winter" here (it gets a nippy 55...ptthh), then it kind of just sucked. Closed registers and our room was sill chilly but the attached bathroom was blowing like mad. So the last two years we close the bedroom register, fully open the bathroom's, open that door to the room, and we're warm...but power bills went through the roof. I climbed up there 2 weeks ago chasing Romex runs and just happened to notice that a duct was not connected...at all. It just happened to be right off the heater and into two bedrooms; which were culprits to begin with. An inspector had been up there, climbed over it, and obviously sat on it to separate it. We've been heating the attic.
See anything to look into? My first would be to see if all ducting is fully connected. Anything 80's and up is many rigid plastic ducts spread about and connected by rubber boots. Take one boot off anywhere and that's where all the air is going to want to go. Not out the register, but perhaps behind the dash. If you can pull the radio unit, that's where a main header usually is. You're getting cold air, just not a lot of it...so the A/C is working. The next would be to think about where the blower is in your car, if you can get to it easily (post-90's, no), and if it's dirty or not. A squirrel cage has a flaw in that just a fine coverage of it's fins can drastically reduce it's output. Our vertical fans in the house need blown out weekly just because we have cats...
Just some things to think about before jumping in with patch jobs. Maybe the blower just needs a little oil. I don't know...I'm waaaaay over here