I've done an IR analysis on both the Evo IV and V to compare their timings...
Myogi- pretty much the same..2'55 to 2'56 range
Usui- Evo IV is better by 1 or 2 seconds on both directions
Akagi DH- Evo IV is better
Akagi UH- Evo IV is better as well...Evo IV takes akagi as well.
Akina DH- Evo IV noticeably better by 2 whole seconds.
Akina UH- Not enough times recorded here to make a comparision, but it seems Evo IV is also better here. Evo IV takes akina as well.
Iro DH- Obvious. Evo IV is better
iro UH- Evo IV as well.
Akina Snow DH- pretty much equal, unfair to make a comparision, but Evo IV's timing is slightly better.
Akina Snow UH- Evo IV again looks better
Happo Inbound- Evo V is better here
Happo Outbound- pretty much equal
Shomaru Inbound- Evo IV blows away Evo V
Shomaru Outbound- Evo IV noticeably better by 2 seconds
Tsuchisaka Outbound- Evo V is better by a second.
Tsuchisaka Inbound- Evo V also better here.
So the Evo IV is better for usui, akagi, akina, iro, and shomaru (Evo IV blows the V away on usui, iro and shomaru). For myogi and akina snow, both cars are pretty much equal. Evo V is better for happo and tsuchisaka (but only slightly). So you can sayEvo IV is the best Evo. HOWEVER, Evo V reportedly has a better start-up, and start-up is all important in this version now. This makes the Evo V theoretically better for battles.