Full-Text Indexing frequency

A while back, I had a question about whether Full-Text Indexing set to 
immediate was going to completely torch my server (it hasn't, but it's 
been noticeable at times).  I appreciate all of the replies. 

Now I've been told that that the indexing doesn't need to be immediate - 
every ten minutes would be enough.  I'm of the opinion that this change 
would make very little difference.  However, I did look into it and it 
appears that I would have use a program document to call Updall 
periodically because only the Scheduled option for update frequency would 
allow an "every ten minutes" choice.

I'm curious what difference this would make on the overall resource 
utilization on the server.

Would it be better because the index would update to include all documents 
arriving over ten minutes rather than updating with each document?  If so, 
would it be significant?

Would it be worse because the program document would be running against 
all of the mail files and so all indexes would be updating at the same 
time rather than being staggered naturally by the messages coming in at 
different times?  They appear to run consecutively rather than 
concurrently, so I'm picturing a single thread busy for a long time rather 
than several threads running all at once, so it's not literally "at the 
same time" -- or is it?

How would the schedule be affected if the process to update the indexes at 
(for example) 3:00pm took fifteen minutes to complete?  Would a new 
process spawn at 3:10pm to update indexes again?  Or does the server wait 
until ten minutes after the previous process completed, so it runs next at 
3:25pm?

Also, where should I be looking for data to quantify performance before 
and after such a change was made?

Thanks,
Patrick