SQL Server Version Store Performance differences between RCS and ASI
Just turning on the database setting will affect for how long the versioned rows need to stay in tempdb (since transactions that could be running in true snapshot would have repeatable read). I.e., enabling ASI will keep row versions for a longer time than enabling (only) RCSI.

As for performance for the applications we can't say. Only enabling ASI doesn't change client application behaviour unless they also explicitly ask to run with snapshot isolation. I.e., doesn't change default behaviour for apps. 

Assuming that all your apps consistently are modified to use the snapshot isolation (pretty unlikely) then the performance will be pretty similar between the two. Readers aren't blocked by writers. You can get into edge cases with update conflicts and how they are handled with error handling, re-try etc. But there are so many dependencies here, so that cannot be generalized - and those are edge-cases anyhow so it is highly unlikely that they will have a measurable impact.