To confirm a few things on the 438's (and reinforce what Danny has said). My car is a 172 with PAS, AC, exhaust and the prototype K-Tec induction kit;
Idle - not a problem, very smooth, almost the same as standard. I use the car as a daily and it's perfectly happy sat in the commute.
Performance - I gained 22 bhp and 8lb ft
'Feel' - under 4k a slight difference, with a bit of induction noise. As you go past 4k and into the 5's the car just starts pulling like a train, and the noise is epic, right upto the limiter.
This makes the car very drivable, as if you want to potter along in traffic and save mpg just change up at 3k, if you want to fly around like a bat out of hell or for track work just work the box and your changes differently to hover at 4.5k.
The link to my project thread and graphs is here if people haven't seen it;
http://www.cliosport.net/forum/showthread.php?612638-Cub-172-s-Flamer-Project
Comparable results that I know of, all with 438's;
Laine 16v - 192 bhp
me - 197 bhp
tank - 203 bhp
Looking at Sams results I think both 438's and Gt cams will give a good result if fitted and mapped correctly.
If anyone is unsure on the 438's and is near Reading then pm me and I'm more than happy to show them / take them out in the flamer for them to see first hand.