will 1:8.7 stabilize all bullet weights? likely to use 160 NP.

Yes. That is the twist rate for 1908 Brazilian military barrels. They shot 175 and 139 grain bullets. You may need to slow down 139 grainers to get best groups.

Never shot lighter bullets in 7X57.

My 20 inch 8.66 twist barrel loved 175 grainer Nosler partitions. Most groups - .50" at 100 yards.

My current 23 inch 9/1 barrel likes 153-166 grain silver tips. Shoots 1 inch or less at 100.

I had good luck with 1x9 and 1x10..with bullets from 120 Sierra, 130 Speer, 145 Speers, actually any bullet up to 175 gr Nosler's over many years, my present 7x57 is a Ruger 77 custom by RJ Renner and I suspect its a 1x10 as he used the original
Ruger barrel, and its an incredibly accurate rife with any bullet. For deer Im sold on the 130 Speer FB or BT and for elk the 160 or 175 gr. Nosler partition or lately Accubonds..

I don't know what the twist rate is on mine, but my "specialty" load was 50.gr of AA4350 shooting 145gr Speer Grand Slams..