As we ventured deep into the K-swap, we offer 4 transmission variations for our kits and still looking to possibly add more options

ZF 5-speed transmission was the most economical option, however that has been changing as they have gotten more difficult to source.  So far from personal experience and from our customers, this transmission is capable of handling up to about 550whp.  At 600whp with drag radials on a S14, this transmission called it quits on the first pass.  This trans is the lightest out of the four weighing in at around 72 pounds.
ZF 6-speed comes in next following the 5-speed in cost, size and weight.  Availability of the 6-speed has definitely become sparse and in result the cost has been increasing.  
The 5-speed with the stock 4.10 final on the s-chassis, you're at about 4300rpm at 80mph, so if you plan on driving long distances we highly recommend the 6-speed.  1-5 gears are almost identical with the exception of having a 6th gear.
CD009 is a big transmission as you can see from the pictures.  Length is about same as the DCT and the bell housing is about 1.5" larger in diameter.  With size comes the power handling trade-off.  CD009 has been proven over the years to handle big power from even the LSx V8's and has been a viable option for the T56 trans replacement for many project builds.  This trans comes in at about 125 pounds.
So far on the K-swaps we have seen near 1000whp with our Twin Disc clutch setup with repeated drag launches with zero issues.  You can even purchase the CD00A variant from Nissan for approximately $2200 brand new!  Can't beat that and it's 6-speed so with 4.10 final - gearing is great for both track use and cruising around.
DCT is another big transmission but with 7 gears.  DCT (Dual Clutch Trans) is still fairly new to swaps, and one thing to keep in mind is that you must be willing to figure out the quirks with it.  Although it's marked to be a more affordable option for those looking to go full sequential, it's not a drop in and go setup. The GCU needs to communicate with the ECU to function properly and all of the wiring must be done correctly.  We are hopeful to learn more about the DCT as we are planning to run this upcoming season with one in our S14.