FTR I am sure your beer is great, I'm not saying that your IPA is over oaky. Just stating the fact that if you get a new
bbl, in my experience (and that of many others), the oak comes through extremely fast. In my case I had to pull the RIS out after only 2 weeks. this was back in 2006. I still have this beer in the keg. It's a very nice beer and still has a solid oak character. I can't imagine how much faster the oak will come through in a 5L bbl.
Its really cool you were able to get a used 5 gallon whiskey bbl. I had no idea there was such a thing. I wouldn't mind getting my hands on one of those as well.