I'd like to preface my post by saying that I have taken 40mg of valium about 30 minutes ago. I was accumulating a horrific sleep defecit throughout the week and had the good fortune of being able to take a 5 hour nap this afternoon. I took the V's so that I could fall asleep at a "normal" time. I just wanted to clarify incase my post was incoherent.
Anyway, the biggest factor in my opinion is your recovery time. Squats and deads are both huge compound joint movements. Personally, I can't squat heavy and deadlift heavy both in the same week. I should mention that I know OLifters who squat 4-5 times per week as well as performing a pulling motion (usaully RDL's or clean pulls) 3 times per week. These guys aren't usaully lifting to failure but even so, I could be on a gram of test a week, take 2 A bombs per day, eat 8000 cal/day and still overtrain. Basically, experimentation will be required.
With that being said, I'd recommend the following. Spread out your squats/deads by as much as you can (ex. deads on mon., squats on fri.) Each week, make one heavy and the other light. Switch back and forth. What may even help would be to use an alternative exercise on the lighter movement of the week. For instance, say you just squatted on Monday. The squats were heavy back squats (triples). Come Friday, stand on plates when you deadlift to increase your ROM and do submaximal sets of 6-8 reps. Experiment, use your imagination. You'll eventually figure it out by trial and error. Assistance exercises are easier. Here would be a sample split.
Monday: Squats (or variant).
Possibly heavy walk-outs
Abs/obliques
Tuesday: Bench Press***
Incline dumbell press set at a steep angle
Supinated grip bench press (excellent tricep exercise)
Wednesday: Misc.: Curls, grip (especially vice grip-best carry over to deads), Anything else that seems appealing. ( Keep it short)
Thursday: Rest
Friday: Deads (or variation)
Glute-ham raises
Upper back: You'll probably be too fried to stabalize for bent over rows. Probably do seated rows (wide grip) followed by 1-2 sets of heavy 1-arm dumbell rows.
Abs/oblques (take it easy)
Saturday: Over-head day. I love push press. Follow that up with something which emphasizes the bottom portion of the lift (ex. seated military)
Sunday: rest
***Persiodically work the weak point of the lft. For example heavy lockouts in the rack. Set the pins at your sticking point. You could also do floor presses or 2-3 board presses) If your sticking point is off your chest then do somethink like pause-press, bottom position bench press or bench (lightly) with a cambered bar.
OK, I have no idea if any of this makes sense. I can barely keep my eyes open. I'mm off to bed. Good night.