Inventory Turnover

Hello Group,
I need some suggestions for creating inventory turnover reports. I suppose I'll 
have to query the IM Transaction History File for this and you all know that 
this file grows in size exponentially. My guess is this file already contains 
200,000 records. Here are my questions:

(1) If I were to write a query that is going to pick all 'SA' transactions with 
order type 'CO' and multiply the quantity by the average unit cost for each 
line item to get the total cost of goods sold (this can then be used in another 
query to determine inventory turns), how big a load will this be on the AS400? 
I'm asking this question as I was asked to be careful while querying the IMHIST 
file.

(2) Is the above approach a general practice for creating inventory turnover 
reports? Could you suggest other ways to run an inventory turnover report. 

Your suggestions will be appreciated.

Regards,
Nandu