Having nearly completed my degree in Acc & Fin. and the intention of starting the ICAI exams next year; i'd say in your shoes i'd opt for the ACCA straight away based on purely quantitative reasoning (in my case qualitative reasons encoraged me to do the degree).
I could have started training right away and have progressed to 30-40kish mark at this stage (with 50k in sight upon finishing); however it will now be at least 3yrs before I hit that as im basically at the start of the ladder from a career point of view.
The only reason I did the AF degree was to have the college experience, increase my non-accountancy options, enjoy my youth (I didnt want to start professional work at 17) and to add the long run marginal benefit to my CV. In lay terms... i wanted to travel, party, sleep in and bum about for 3yrs (and by God, it was definitely worth it!)