I have the 1030b (same as 830 except for 2nd 3.5 cage) and finished major modding last week.
1. You want positive airflow, not negative to keep dust infiltration to a minimum (especially if you have pets). Figure on the intake cfm equaling (or slightly more) cfm out.
2. I removed the lower HD cage (kept for later), removed the lower HD drive cage mount (drill out rivets), then cut for a 120mm fan (intake; panaflow L1A) where the HD cage used to be.
3. Underneath, the 120mm fan, I also cut out for an 80mm (intake; panaflow M1A). It is a tight fit, but looks good (take your time marking and cutting).
4. The lower HD drive cage will now be velcroed (for easy removal) on the floor of the case in front of the 80mm fan to keep HD's cool (extra case cooling also). I got the idea by looking at the Lian-Li HD set-up.
5. Cut 80mm (exhaust; panaflow M1A) blow-hole in top of case. Still using the stock twin 80mm's Antec includes in the rear of the case.
This gives me a mathmatical intake of 105cfm (120 & 80 in front underneath upper 3.5 cage) and exhaust of 97cfm (three 80's; not including PS). Very quiet, but good airflow.