the question as above is whether its li-ion batteries you’re already using (I can’t remember if the radio works with both the new and old shape batteries). If its nicad/nimh the longer charge times mean the bigger capacity the better.
The fast charge time of li-ions means (depending on what your working day is like) theres not much disadvantage of lower capacity batteries for drill driving – whatever capacity of battery the spare will always charge faster than you can run the other one down. Even then you can use them part charged with no penalty. They usually get to 80% very quickly indeed, then longer to get to 100% – the charger has a light to indicate that and you get a usable charge in no time at all.
Where the larger 3 and 4amp/hr batteries have their value is with either having more than one tool on the go – say two drills, one to pilot/countersink and one to drive screws, in which case you want both tools to go all day, or for tools other than drivers – angle grinders, circular saws etc those are the tools that need the higher capacity for a good duty cycle, the longer life batteries are of negligible benefit for drill/driving alone.