I think that CT4 will be the most difficult if 103 and 104 were combined into it. I thought those two were fairly substantial courses by themselves; so combined they will be even bigger!
If CT5 is still mostly old 105, I thought it was easier than 104 but that might be personal preference....
I did these at university and we had bits of 104 before 105 and bits of 104 at the same time as 105.
Only thing I can suggest (without checking the new syllabus etc etc) is that if this is what you're thinking of for next sitting; you might as well order both CMPs and then see what fits you best (as the notes won't change before the September sitting anyway; and even if you don't sit in September for any reason I can't see there being a vast change before April 2010).
The CT4 one might be better for you if you like the stochastic side of it as there was a bit of stats and so on in it. Old 103 was covered at the same time as 104 and 105, and a bit even later (it was split into 3 at university).
My course through exams -
107, 108 and parts 102 1st year university
102 (final), 104 (part), 101 ('all' but some covered in 1st year) 2nd year university
103 (part), 104 (final), 105 (all), 106, 109 3rd year university
103 (final), 300 series (all - but not all exempt!) 4th year university
CA3 (201) was not covered at university.
BAM didn't exist (or the new CA2 either...)
