Confused between NB 4 & 5.

Yesterday i tried both novablast 4 and 5 in asics store and got a good feel of both shoes but it left me even more confused. Currently I'm struggling with shin splints which trigger after running for just 2-3 miles and make it unbearable for me to run further, so i looked for some good shoes (I'm not that into running just keeping my health in check) but when i tried nb4 first i felt a little bump behind my toe region which was not awkward but i felt it and the shoe overall was responsive but then i slipped into nb5 and they were soft and smooth but kind of dull in comparison. After trying both I'm even more confused in which one to get. Note: i am trying to run faster to nb4 seems compelling but on the other hand nb5 might look after my shins and joints me :/