Indeed it's a Bf109G-2.
Photo taken on 29 August 1942 the day he achieved his 150th victory.
I'm not sure he was "acting" command of JG 52 since he was in Charge of JG77 since earlier May... But I don't know all and I, maybe, haven't the right book. (Source photo: eBay)
I thought he just made his 150th in this plane, that' all. I don't have all necessary documentation.
Correction: Hmm .... according to Holm's site he was acting Kdr of JG 52 effectively. Which is not indicated here:
http://www.luftwaffe.cz/gollob.html.
Note the machine has a III.Gruppe wave marking.