Not 70-80% that's way too high, 50% at best.
Akainu's magma is EXTREMELY dangerous, one slip up by Luffy and he can could lose an arm or a leg or get burned through like Ace did.
Not to mention we haven't even seen Akainu's awakening yet which must be catastrophic considering it permanently devastated half an island. Also Akainu can take a helluva a beating and still keep going, though Luffy has been displaying some impressive endurance feats lately it's not equal to Akainu's.
Luffy will need to seriously get his Haki and stamina game up to face a guy like that.