If I may, I think you're comparing apples, to oranges to bananas.
The Speed is a lower AR wing with more of a freestyle nature compared to the near thoroughbred race design of the Chrono. The Frenzy, even more of a departure from both the Speed 4 and Chrono. The 13m Frenzy is less of a light wind rig and more a kite for a "Clydesdale" class rider. The jump from the 15m Frenzy to the 18m Chrono is considerable.
The Chrono is a high performance race style kite. We have a 15m in our demo fleet and will have the 18m in soon although we questioned if it was even needed based on how the 15m flies and pulls in wind that you can't feel even on your face.
The 15m in the limited flying time I've had on it so far is an unbelievable efficient machine. It build apparent better than any kite I've ever seen apart from maybe some Elf models and those have a much narrower wind range. It is easily better at building apparent than any of the previous Speeds have been but with much more grunt. Which for me at 200# the Speeds always seemed lacking. We will hopefully get a chance to do a side by side comparison with the Chrono, Speed and in the same vein HQ Matrixx 2 this winter.
The Speed is obviously and incredible kite. Flysurfer has dominated to light wind realm with those kites for ages and anyone who's flown them will attest to how good the kites are. Me personally I'm a fan of the 19m Psycho 4 SA DLX for light wind because I like maneuverability as well as light wind ability. And the Psycho holds it's own against the Speeds but you have to work it. This said the 15m Chrono, is way beyond the 19m P4 DLX in light wind performance.
The Summit 15m in UL might be a good option. Though not nearly as good in light wind as the Chrono, not even the 15m but it will be more versatile and more user friendly. Not as good in light wind as a 18m Speed 4 but pretty good.
As I mentioned another option would be the Matrixx 2. We found the Matrixx 1 to be a damn good kite in light winds even with 15m being the largest and being made of standard rip stop vs. UL. We always though they should make it in a UL version or go up to 18m. They did both.
This year the Matrixx 2 comes in UL 20d lightweight and is offered in an 18m. More of a direct competitor to the Speed 4 than the Chrono. Really the Chrono is in a different class than any of the other kites we've discussed so far. The Matrixx 2 is a similar AR and design philosophy but at a lower price point.
I guess the question comes down to several factors. How light a wind do you want to ride in? What's your experience level? (The Chrono, good for advanced riders tough for most others) What do you want to do with the kite i.e. where do you want to ride? (snow/water/dirt) What's your riding style? And what's your budget?
There's another kite in the Flysurfer option that I'm not able to discuss until they do the new release on the 1st. We don't have all the details yet on that one.
Light wind kites are a tough call. Sucks that light wind kiting is also the most expensive. Any of the kites I've listed will add to your riding days but you might get lonely being the only one riding while everyone else watches.