Greetings,

How big is your room? 

I would not recommend the 4B's as the front mains for anything expect maybe for an extremely small room as part of a 5.1 system or maybe a computer station monitor.  Not only do you get a lot more bass from the 4T's but you alos get a lot more midrange.  They are going to open up your soundfield quite a bit over the 4B's thus filling your room with more sound and providing you with a more immersive/expansive experience.. The difference would not be subtle.

Go with 4T's for now  and add a sub later (choose based on room size).