have a look at the sniper sling stuff. never in all my life have I seen bands with such a high stretch ratio. 150 mm
I have tried several, but far from all, the latex brands out there. I saw when the snipersling came out. I think a few of the web sites had typo's for the elongation ratio which is pretty common. The snipersling page lists the elongation factor as 6.5 to 7 (
https://www.snipersling.com/products/snipersling-super-fast-latex-band-for-slingshot-shooting-200cmx15cm-rolls). This is at the high end of stretch ratios but maybe not so different from the stretchier GZK versions or Precise 3rd gen. The snipersling site also claims the bands are ~5% faster than other brands. May be interesting to try them out and see if this is the next incremental step up the ladder, or if it is just pretty much on par with some of the other good ones around.
In my experience, personal preference for the feel plays a big role. Some people like the stretchy bands with high elongation ratios and some people like the stiffer ones with lower elongation ratios.
After looking at several with with a chronograph, brands like Simpleshot, Gong Chi (green), and Cattyshack that are stiffer and work best at ~470-550% elongation are among the fastest if not the fastest around even for having relatively short stretch ratios. Although again, none of these are 10% faster than the higher stretch ratio elastics. And if the really stretchy elastics are well optimized for active length, I believe they catch right up or are not more than a few % off. In my hands, Precise 3rd gen is a real dog at 500% stretch and lags clearly behind the others there. But it gets pretty fast for me when I use it at stretch ratios at or over 600%, and while I haven't tried pushing it farther it feels like it could still stretch even a bit more.
So in the end, until a revolutionary new elastic moves the bar significantly up I think it is all about finding a brand that feels good according to personal taste and then optimizing the active length. And the active length can be tuned for outright maximum speed or an optimal balance between speed and band life.
Get a currently respected up to date brand that feels good for you and get the active length right and I doubt you will be 5% behind whatever the hottest band out there is.
Just my thoughts. And while offering them I will admit I am always on the lookout for the next hottest band that will send my ammo out just a bit faster than anything I am using now. Although this tends to produce more rabbit holes than true advances. At least for me.
