F-5XC size and dividers

I have an F-5XB and love it for the usual reasons - size, inconspicuous, shoulder strap, look, quality, etc.

I load it wth ---
a Nikon D40x,
nikon 18-55 lens,
nikon 55-200 VR lens,
sb-400 flash,
2 circular polaring filters, spare battery, lens cleaning tissues and a cloth and spare SD cards hang from the shoulder strap rings.

I'm thinking that a F-5XC would also let me carry my sigma 70- 300 lens and perhaps a 50mm f1.8.

Also, I figure that I'll need padded inserts and/or dividers.

I'd would appreciate your opinion/recommendations about the F-5XC for my kit.

And if you would let me know which inserts and divders are compatible with the bag and how can I get them.

THANX