Thanks for the reply, that make sense since I never ran into any problem, I think I will skip this time and wait for the BIG 4.0 update.
Side note:If I do decide to go with 3.1.3 and 5.11, is it how you do it?
1. Install OEM ipsw3.1.2 BB5.11
2. Install custom IPSW 3.1.3 and retain the BB5.11
3. Unlock with either ultrasn0w or blackra1n