I'm trying to estimate the cost benefit of such an upgrade.
Well, that really depends on usage and size scenarios and thus can not easily be answered.
But I would consider it reckless to run a Raid 0 on a 960 EVO which is extremely brutally READ optimized - the daily write allowance on thsoe drives is a bad joke. Not that they are bad drives, but they are very clearly intended as boot drives for laptops, normal computers etc. Heck, even the 960 PRO is not really suitable for server work.
Regardless of performance, I would consider this a reckless crossgrade to unsiotable equipment. Gather a real server level M.2/U.2.
And again, the question relly can not easily be answered as it depends on usage.