Depending on the amount of traffic you receive, there should be no difference in resource usage with max_children set to 6 vs 50. (Baring your the other values are the same as before)
But with 50 in max_chrildren, php-fpm would fail at around 8 spawned children, which would take everything down due to lack of memory ? Having it at 6, the only thing happening is that php might timeout, but the rest of your vps will to some extent function normally.
Also, the 50% CPU usage sounds like a spike after a service restart. I would suggest running something like this:
echo $[100-$(vmstat 1 2|tail -1|awk '{print $15}')]
That one should update every 1-2 seconds with current %cpu load.
Best of luck in any case, and don't hesitate to ask if you need more help.
