Yes there is a difference because the data for a long record might be running into multiple blocks, where as the data for a small record might be in just one block. This way when we you do a select the number of blocks that are needed for the select will vary. This will be true in inserts too. Try to increase the block size this will improve the performance.
Spool is nothing but blocks of space that can be used. it does not matter if it is a big record or a small recrod as long as the data can fit in the available spool it should work, once it exceeds the space you will run into spool error.
Just for your information, when looking at PERM and Spool space think of the following: Perm is like a the fuel in your cars tank when you reach it you job fails. Spool on the other hand is like the speed limit ,every one can travel at this speed with out too much problem.