Improving performance of EXTRACTVALUE XML DB

I have posted many times here in the last few weeks.  The main problem I am have is this select statement.
If I have a count of 5000 as above then I have to crate a loop from 1 to 500 where I pass in i . The bellow statement takes more then a second.

select EXTRACTVALUE(SYS_NC_ROWINFO$,'/PDATA/EVH[i]') "EVH"
from XMLTABLE
WHERE EXISTSNODE (SYS_NC_ROWINFO$, '/PDATA/EVH') = 1;

I will have to process 640 million recs in 8 hours possible? Files will arrive in no greater then 1.5 MB.

if the above takes 2 seconds.
What I retrieve is <EVH>1~2~3~4~5~6~7~8~9~10||1~2~3~4~5~6~7~8~9~10||n times </EVH>

This has to be parse using || delim which represents 1 rec.
This has to be parsed 1~2~3~4~5~6~7~8~9~10  using ~ then inserted or update a table.

So far the EXTRACTVALUE is the bottle neck I really need to improve this. I just posted another question on how to register xsd to see if that will speed thins up.

I am also directly loading xml file into a clob data type.

I basically have two approaches load to xmltype table or direct from xml.

Because the xml file is fairly simlpe 3 tags 1 of which has embeded || and ~ does it make more sesne to build my own parse using instr to sepreate out hdr , evh and evd tags.

I am storing the parsed values in a nested table, is this the most efficient, maybe varray?
Could the temp values be stored in memory to avoid disk reads.
Can I use bulk loading techniques?

Also I am working on a database that was setup by someone else.
There there are only 4 tablespaces
system
sysaux
undo
temp
the system and sysaux are 99% full. This will slow processing down for sure.
The table and index are also use system table space, I can create new table space for table data and for index.
We do not have tablespaces on different disks. That could be an improvement placing tablespaces on diff disks.

Does the XDB schema default to system tablespace? Should that have its own tablespace?

All the code is on www.ihos-t.com/code

Lots of questions, in crisis mode at this time. I don't think it can be done but I want to get to a stage where at least its not dog slow.
Thanks in advance.