sqlite varying write and read latency

In my C application i am moving to sqlite DB.Am doing experimentation on the said DB.I maintained 1 Writer process and 3 Reader Process.Total records i have is 126220(these are not read from file;these are given to process at somepoint during the lifetime).

These are my observations.
1)when i have the following table structure(Journal and synchronous set to OFF )
create table if not exists table1(col1 int primary key,col2 text,col3 text ,col4 text,col5 BLOB)
Write and read time taken is 25.814 seconds and 5.806 seconds respectively.
2)when i have the following table structure(Journal and synchronous set to OFF )
create table if not exists table1(col1 int primary key,col2 text,col3 text ,col4 text,col5 text)
Write and read time taken is 70 seconds.
Why is the difference here? I am assuming that it depends on the total bytes to write.
3)When single read is done time taken is 5 seconds ,but if i do a parallel read the same is done in 3 seconds.Again why is the difference here.