I'd also ask yourself what direction work wise you'd like your flying to go
With the CPL theory you could eventually become an FI
If you decide you'd like an IR (subject to the validity period) you'd need to sit the IR theory exams if you'd only passed the CPL theory
, whereas ATPL theory would be sufficient for the IR also
. (Only madatory multi crew is North Sea and they'd want an IR for both crew members, and the onshore companies that regularly fly two crew also want IR's)
IMHO do the ATPL's and keep your options open. I see little to no point in merely doing the CPL theory.