Well, it seems you are used to one muscle per day with a lot of volume. Since that is working for you, I'd recommend sticking with it, but changing your exercise selection. Usually the first year or two you'll gain no matter what. However, at some point, your gains will plateau. This is where the increased frequency comes in. For now, I'd recommend looking at a program like
OVT: Optimized Volume Training. You keep the once a week frequency (because it's working), but the exercises are more optimal. Here's the program:
The OVT Program:
DAY 1- Chest/Back
Day 2- Legs/Abs
Day 3- OFF
Day 4- Biceps/Triceps
Day 5- OFF
Day 6- Deltoids/Traps
Day 7- OFF
The Routine:
http://www.t-nation.com/readTopic.do?id=459276
Day One
A1-Bench Press-- 5 x 5, tempo of 2-0-1, No rest interval
A2-Flat Dumbbell Flyes--5 x 5, tempo of 6-0-2, 120 seconds rest.
B1-Incline Bench
B2-Incline Flyes
C1-Lat Pulldown
C2-Pullovers
D1-Barbell Rows
D2-Seated Cable Row
Day Two
A1-Front Squat (same)
A2-Lunges
B1-Machine Squat
B2-Leg curls
C1-Deadlifts
C2-Calves
Day Four
A1-Barbell Curls (same)
A2-Dumbbell Curls
B1-Preacher Curls
B2-Hammer Curls
C1-Weighted Dips
C2-Triceps Extentions
D1-Cable Pressdowns
D2-Reverse Curls
Day Six
A1-Barbell Press
A2-Wide Grip Upright Rows
B1-Machine Press
B2-Side Laterals
C1-Bent Over Laterals
C2-Machine Rear Delts
D1-Shrugs
D2-Close Grip Upright Rows
Basically, what you have is a total of 100 reps per bodypart. Every set is in fact a superset of two exercises working the same muscle group.
The first exercise in the superset is a big compound movement (e.g. bench press, squat, deadlift, row, even clean or snatch) and it's done for five reps using as much weight as possible.
The second exercise in the superset is an isolation movement for the main muscle being worked in the first exercise. This second exercise is also done for five reps, but with a small load and a very slow tempo.