Changed my carrying possibilities yesterday and thought I'ld share my first impressions.
Old Setup: performance transit bag
transit epic dx
3 outside and one top compartment
decent carrying room
have to either use 4 velco straps or bungee net to fasten to rack
after 5 years, zippers start failing
New Setup: topeak bag
Monster main compartment
Even with winter gear, haven't had to use pannier function yet
very nice reflective strip
shoulder strap if loaded heavy
different size zipper knobs, so you know if you are opening or expanding the bag
nice carry on handle
outside dimensions are about the same as the performance bag, but better utilization of space
since bag slids into rack, you can open it and throw stuff inside, or rearrange without having the bag fall on the ground
again just one ride, but using seat post beam rack, 5 mile ride time dropped by 60 seconds. I think this will be constant, but will provide more information after I had had time and weather to complete a cycle of 15 commutes.
Only disadvantage was initial cost, but thanks to an REI $20 special, I decided to go ahead.
For those who saw other posts, yes I was considering a trek bag and rack. But local trek store is mtb store. "aero doesn't matter, you have to be going more than 20mph for it to matter." Goodbye trek. Hey I learned math. 10mph rider and 10mph headwind means aero does indeed have a significant effect.