Igneel, in a weakened state, was able to give Acnologia a good fight (guessing that at full power they're almost equal), and he has some pretty good DC feats from what we saw (plus the advantage of flight).
Round 1: Igneel stomps.
Round 2: if he goes straight for the roar, Igneel stomps. Otherwise, he still stomps, but it might take a little longer.
Round 3: Igneel stomps as soon as he decides to go for the roar.
Round 4: Igneel wins with very little difficulty.
Round 5: Igneel wins with mid difficulty.
And he stops at round 6, putting up a good fight against Kurama but eventually going down.
Needless to say, the Juubi would crush him.
Stops at 4 IMO, but I could be wrong
Do you think Igneel can get past Shukaku's regeneration? I mean Gamabunta cut Shukau's arms off, and later Shukaku grows them back. Legend says bijuus are immortal because of their regeneration ability
Let's see what good that does him when he's blown to sh*t. No way is Igneel losing to Shukaku.
He may be able to clear shukaku, but anything above that is clearly beating him.
I can't see any possible scenario where he couldn't clear Shukaku.