OK, here is some Chrony result.
6 degrees Celsius, so no records are to be expected.
12 kg draw weight on both bands,
2,8 x 1,8 x 23 cm two bands per side old TBG
3,8 x 2,4 x 23 cm two bands per side new TBG
15 mm steel:
old TBG 64-68 m/s
new TBG 67-71 m/s
16 mm lead:
old TBG 54 - 57 m/s
new TBG 56 - 59 m/s
The new TBG is slightly better than the old type (yipeee).
But of course you have to cut wider stripes (or use more layers) to get to the same draw weight.