My god this has gone way off topic, if you need 3500 to spool a set of -5s compared to 2500 for the -9 than the -5s are obviously more laggy end of story
Now to answer the original question
To reduce lag the following things will do it and the amount of money it costs verys
Cam gears, exhaust sizing, compression ratio, increase capacity, removing inlet restrictions (if present) and fit smaller turbos.
That is how you reduce lag, which ones you chose to do is up to you