Comparing Splunk, ELK & Metron Hadoop

We are considering Splunk, ELK or Apache Metro Hadoop  for SIEM.

Q1:
I've encountered nightmares with a top-end SIEM in the past when
querying/retrieving data : takes days & even crash : which of the
above has excellent super-speed log management & querying?

Q2:
I was told by an ex-colleague that Arcsight/Splunk requires CEF
(Common Event Format or syslog format) to be piped to them
as they can't accept any other format.  A vendor using QRadar
told me QRadar requires syslog/CEF format inputs too.
I've SNMP traps / MIBS events (eg: from Cisco & proprietary
devices) that my ex-colleague told me can't be accepted by
Splunk/Arcsight, so would like to know if any of the 3 above
tools are more readily able to accept other SNMP/other
event formats

Q3:
Heard that ELK lacks policies which in the long run will be
costlier if we get consultants to customize : do the other
2 products have this concern.  
Also, Splunk Enterprise goes by amount of logs & we're
concerned that too much logs (can be 500MB/month)
 will make the cost high:  weighing between customization
/set-up PS efforts & licensing costs based on amount of
logs (which I guess we can archive off older logs to reduce
the license cost), which of the 3 are more cost-effective?