connect to 11g database is slower than 10g

Here is a script I am using to test connection with 11g database and 10g database

#!/usr/bin/sh

counter=500
date
time while [ $counter -gt 0 ]
do
   sqlplus <<-eof > /dev/null
     userid/password

      quit
eof
   counter=`echo "$counter - 1" | bc`
done
date

I tested this connect to 11g production database on AIX 7.1

oracle@pclcdb01:/home/oracle/acn9089> ./test.sh > test.log

real    1m7.39s
user    0m12.92s
sys     0m7.60s

I tested this connect to 10g test database, on AIX 5.3

oracle-TEST@pclcdb99:[tcrs_ua1]:/home/oracle/acn9089> ./test.sh > test.log

real    0m29.16s
user    0m8.56s
sys     0m6.99s

Can anyone explain why we have a lot difference? Thanks.