If you watch the Spoon K20 Ek9 around Tsukuba you will see that its not as quick as the Spoon B series Ek9 although the B series version was probably built in the late 90's early 00's
No doubt the K20 has more tuning potential but in my opinion the feel, the noise, the excitement you get from the B series will never be beaten AND they are easier to work on AND they are a direct fit.
Just as an example my B18c Ek9 I had before the Evo had an RMF manifold, Custom 2.5'' MidDevelopments Decat and cat back exhaust, ITR filter and a cold air feed with the stock map.
My friend had a K20 Eg with 2.5'' exhaust, kswap manifold, kswap filter, k100 mapped and a dc5 box.
other than him having the edge on the top end we were evenly matched. Think the comment I got before hand was ''Smokey B series isn't any match for Kswap''
Just goes to show every car/engine will differ and some faster than others.
Like I say B series hands down for me.
If I was to get another Ek9 I would do what I was originally going to do, High Comp B18c with a built box which I had most parts for but then sold everything on.
Now I have the Evo and it is nowhere near as fun as the Ek9