I currently have a 2013 slice 105 (58cm), can anyone give me an idea how much faster a 2020 P-series 105 (58) would be? I'm also open to other TT bikes around 4500 CAD$.

I know wheels also matter but lets say they are the same. I have a good aero position that I think would be easily transferable

I usually make up time on tight fast corners and down hill so the disc brake really appeals to me. Also having a box is good because I'm getting into longer races now and I don't like taping GU to my top tube

would spending an extra $2000 get me a more slippery bike? If so how many watts are we talking?

Thanks for any help :)