So is their a similarity, Looking at taking both in March 2018
best choice is not to... take them together... go for F7 and F8 as the are both a bit tough but have a partnership between them as F7 IFRS knowledge is required in F8
It is not that bad combination but as far as i have heard, F5 has turned out to be a very difficult paper and F7 being financial accounting is itself a tough one. So if you think you can manage both and can prepare for both of them in the time you are left with, then go far it, else don't.
These are just two papers so can be taken at the same time but if you study them properly and if you have that confidence to pass them.