Fixed or single speed

My 2p.

I've ridden the same bike through town for the last year. Pretty much half SS & half fixed (with same brakes). I average almost exactly the same time fixed as I did SS, though I have been fastest fixed.
I doubt the same rider would have any noticeable speed difference round a corner. I think the assumption that pedalling buggers up balance is wrong - for an experienced fixed rider 20mph is easily acheived spinning smoothly.

I have found that I can take corners faster by coasting.

My fastest times for the same journey have been on a geared bike, but I best not mention that here.