From what I can see Dynaflight 10 is not a current BCY product (at least it's not listed on their website any more) and it's made of Dyneema SK78. Dynaflight 97 is still made (and available from a number of the usual UK retailers) and it uses 100% Dyneema SK75. SK78 is said to be more resistant than SK75 to creep (which is permanent elongation) and stretches less (i.e non permanent elongation) under tension. Creep is unwanted, while some stretch/elasticity is probably wanted, at least in recurve applications. Bear in mind most of the time bow strings are massively over-specified, i.e. one strand of Dynaflight 97 has a break strength of 120 lbs, while typically you'd be using 14-16 strands of that material, so creep caused by the material itself elongating should be pretty minimal TBH. There's some technical comparison of the two materials here (about sailing ropes) - http://www.samsonrope.com/Documents/Technical%20Bulletins/TB_Understanding%20Creep_MAR2012_WEB.pdf
The 10 is basically a dyneema (but a later formulation) same as the 97, 8190, 8125 etc...
but the strands are thicker. So where you might use 16 or 18 strands of 8125, mid 20s on 8190, you'd be looking at 12 to 14 of Dynaflight 10.
So, D10 is five pounds stronger, creeps a little less and costs $8.00 more than D97 for a 1/4 lb. spool.
Here is the response from BCY.
Dynaflight 97 is made from, what was, the best Dyneema yarn, SK75. Tough and durable. Low creep. Used on compound and recurve bows.
Dynaflight 10 is made from what is now the best Dyneema yarn, SK78. Very little difference in strength and durability but even less creep. Same size as D 97. Same colors available. Just a little better product because of the lower creep.
I got in some Dynaflight 10, and built a few strings with it. I had to make my string 1/2 inch longer than my normal dynaflight 97 strings. When cutting my flemish strings I can tell the dynaflight 10 is stronger (harder to cut). So far a lot less creep with the dynaflight 10. I have shot some arrows through the string and don't notice any difference in sound, but my arrows are acting slightly weak now. Not a huge difference, other than there is very little creep with the Dynaflight 10. I will see how the strings act over time."