A fpm pool of 4 for 1 worker is more then enough to have the same performance with win32 compared to linux, of-course linux supports more workers but you can get that on win32 too by loadbalancing multiple nginx installations using nginx itself in fpm frontend mode to multiple nginx backend nodes as, affinity managed, fpm pool.

Why php aborts depends on whats happening, have a look at php's timeout settings and "ignore_user_abort = On". Add a loop label in the batch so it restarts the cgi process. I haven't yet had a fpm process terminate while the pool balances nicely to the amount of requests.

Use ab.exe(apache tool) to benchmark and tune things.