I joined the Uk Himalayan facebook group long before buying mine and the concerns you mention ie lack of power and wind buffeting are on there.
From memory there were a lot of comments about the engine being tight for the first 1k miles or so but a noticeable improvement from then on.
The lack of power was a shock to me but had I had a test ride then I would have known that. In all honesty I may not have bought one because my head was fixed in the 0 to 50 in 3 seconds before changing into 2nd gear (whilst looking for cameras and cars) mindset so I decided to just buy a used one (3,700 miles) and ride it for 3 months, only 2 weeks in so too early to tell.
You've had recent experience of smaller bikes so the change will be less dramatic so go get a test ride and ride it like you intend to use it.
Buffeting and screens are also mentioned on the owners group page. My standard screen was cut down by the previous owner hence I don't get buffeting just a healthy dose of wind on the chest that let's you know that you are at the national speed limit
![Very Happy :D](./images/smilies/icon_e_biggrin.gif)
. Having had big bikes with Wunderlich barn door screens (with added buffeting) and others with bikini screens I know my preference. On the Himalayan some have found a way around the issues by lifting the screen up very slightly to reduce the air pressure difference which causes buffeting. Again I would say test ride a bike the way you want to use it.
Open your eyes and you see what is in front of you, open your mind and you see a bigger picture but open your heart and you see a whole new World.