which will be faster? w/ or w/o indices

I understand that if you are importing data into the database
that this will go faster if there are no indices against the
target table.

If I want to run this statement:
INSERT INTO table_a SELECT * from table_b WHERE value_1 BETWEEN
X AND Y;
is it best to do that with or without indices?

AND, if I want to run this statement:
DELETE FROM table_B WHERE value_1 BETWEEN X AND Y;
is it best to do that with or without indices?

We are using v 7.2.1 on a Sun E4500.

TIA,
val