A search will tell you that you'll lose a few ponies on the top end, but does it really matter? If you want a lot of horsepower, you own the wrong bike.
P.S. I've been running boom tubes for a few years, and I have no complaints about power loss.
I established that I knew there were some ponies lost. I established that it really didn't matter, but I was curious about specifics.
My search turned up no meaningful data, just vague impressions similar to mine. If you have some actual data, posting that would be helpful.
I think most people would agree that 130ish horsepower for a motorcycle, though subjective, would generally be considered "a lot".
Your lack of complaint about power loss isn't particularly relevant to what I was asking.