If you're doing the individual OE, and you think he can handle 3rd after a brief review, start him in 3rd.
The program is broken up into chunks, with 3rd starting a new chunk. Because it's an expected entry point, there's a ton of review at the beginning, even if you got there by working your way up from 2nd. If you're in the group OE, and have the gifted setting on, you get less review of the stuff your kid knows. My kid was annoyed by the amount of review in the non-gifted setting, and you don't have the option in individual OE.
As a data point, it took my DD something like 13 contact-hours to do half a year of material in the individual OE.
(Reading what other kids are doing in 4-5 hours, if I had it to do over, I'd have done the group enrollment - even though I knew we wouldn't need it for the year. The pacing really bummed her out.)
