It is my humble request to you to go for both the groups. By giving both the groups, you can avail the benefit of set off. so if you score exemption in group 1 and next time when you give group 2 an it goes average, then SFM exemption can take over the line.
5 Months are more than sufficient for both the groups. You need to study smart and make a good strategy for each subjects.
Keep 2 subjects going at a time - preferably 1 theory and 1 practical.
For Costing (AMA) - Study Module, PM and RTP is the bible for us. Cover it well. No need to study anything other than ICAI study Material. For advanced practise of OR, refer sanjay Aggarwal's OR book. Again, Study Module is sufficient.
For ISCA - Make chapterwise summary notes for your revision and quick recap of concepts - cover all bullet points and explanation in easier terms for complexed concepts so that on exam day, you dont have to study the whole text.
For IDT - Refer Yashwant Mangal's book. It is precise and most effectve rather than tangling youself with Bangar. By the Way, Yashwant mangal's book is an organised and precise form of bangar's IDT book and perfectly covered. I referred to this book and got 64 in Nov 2012. It is easy to revise also due to its tabular and digramatic presentation. (ii) Study amemdments and case laws from RTP and amendments book and cover them while doing that particular chapter to with it is related to.
For DT - Refer case laws, amendments, Summary module of vinod gupta. You need to study Assessment procedure, penalties, Capital gains and Income from Business and profession in details and nothing better than vinod gupta's modules. Keep a highlighter with you so that you can revise quickly during exams.
For Group 1 (other than SFM) - Continue with you current study materal.
PS: I got 190 in grp 1 and 233 in grp 2. Passed using set off. My marks in grp 1 were 43, 60 (SFM), 42, 45. So you can see, i benefitted from giving both the groups.
All the best and Happy studying!!