I personally wouldn't do "chest/shoulders/triceps" and "back/biceps" on consecutive days. When you work chest, you work shoulders. When you work back, you work some shoulder as well. To avoid overworking the shoulder, I'd put a day in between (either doing the lower body workout, or cardio).
I think doing a split more than 2x/week is overkill, and it would be hard to fit it in, don't you think?. It probably can be done by some people, but I doubt that they are lifting as heavy as they can with each workout (not enough recovery).
FOr a two-day split (like the Pyramids), you could do something like:
Day 1: lower
Day 2: upper
Day 3: cardio
Day 4: stretch
Day 5: lower
Day 6: upper
Day 7: cardio/stretch
If you tried to do a 2-day split 3 times, you'd be doing a weight workout 6 days a week--if you stick with a 7-day week, which isn't necessary...see below). Not much recovery time. It's doable, but you'd end up using lighter weights. If you don't want to build as much strength/size (I'm not talking "hugeness" here! just tone/sculpting size) this could work, but then why work out so much if you don't want to get the gains?
For a three-day split, I like to do:
Day 1: upper 1
Day 2: cardio
Day 3: lower
Day 4: cardio
Day 5: upper 2
Day 6: cardio
Day 7: off/stretch
You'll notice I put as much time between the two upper body workouts as possible. That works best FOR ME. I have a touchy shoulder, that likes more recovery time, and if I did upper 1 on day 1 and upper 2 on day 3, it wouldn't get the recovery it needs. I also wouldn't be able to lift as heavy on upper body 2, and I wouldn't get the strength gains I do.
You might think like this looks like "not enough" strength training, but if you are lifting as heavy as you can, you need the recovery. Someone (I can't remember who) stated it very well: "weights are the architect, recovery is the builder." The resistance work alone isn't what builds muscle, it's the challenge/stress/resistance combined with the recovery needed to build (recovery including rest, lighter workouts, sufficient sleep, and nutritious food).
Back to the "days in the week." It's typical to set up a rotation using the 7-day week, but that's not necessary. You could set up a routine like: day 1: upper body, day 2: cardio, day 3: lower body; day 4 rest. Or day 1: lower, day 3: upper, day 3: cardio; day 4: rest. And repeat this cycle. That gives you an "8-day week."
(You may want to add more cardio than I indicate, or do cardio and weights on the same day sometimes. The above suggestions are just that: do with them what you will!)
