Initial speed is very good (5-4)
I believe the answer is:
first-rate
'very good' is the definition.
'first-rate' can be an answer for 'good' (thesaurus). I am unsure of the 'very' bit.
'initial speed' is the wordplay.
'initial' becomes 'first' (similar in meaning).
'speed' becomes 'rate' (both can mean pace).
'first'+'rate'='FIRST-RATE'
'is' is the link.
Can you help me to learn more?
(Other definitions for first-rate that I've seen before include "Top-class, excellent" , "Prime" , "Of the highest excellence" , "Top-notch, excellent" , "Start fire to be really excellent" .)