I've requested a 2 sided front pannier which should solve the handling issue and combined with a large seat bag would give you a reasonable amount of cargo capacity.
Following an old post from Alex Wetmore -- I think -- I use a Carradice SQR bag on the rear and panniers on the front on my NWT. When I am desperate to hold more stuff, I either mount a handlebar bag or put a saddlebag (above the SQR bag and mounted on the saddle) on or both. The combinations work pretty well.