I'm going to go with a bit of a wordy post, because power gaming is something I'm trying to recover from myself and that I feel I have a reasonable insight into
It's really important to understand why he has built his character in a way that's disrupting the game and not just 'how to deal with it.' No one worth playing with thinks to themselves 'I'm going to build a broken character and spoil this game for everyone' (I'd bet good money your friend at the table doesn't)
A DM who understands this is in a position start asking why someone is playing in a way that lessens the enjoyment for the others at the table (or you as a DM) and get the opportunity to help players grow, and to grow as a DM in the process.
People power play for loads of different reasons, but it all comes down to the big issue that they don't understand what D&D is about, they see it as something other than a role play experience (usually as a 2D puzzle game, or a some form of challenge without real living beings to interact with)
You will go a lot further working with the person on fleshing out their character and getting them to act in character as part of the story than you will working with them on their abilities which they already see as 2D and want to get the most out of.
What struck home for me was reading Darths and Droids and someone calling me out as being the player who acted like R2 did in the comic
http://darthsanddroids.net/episodes/0001.html
If you show them the way they are acting, and present them with the alternative, you haven't just dealt with a single (or even group of) deadly abilities, you've helped someone learn to play the game in a new and ultimately more rewarding way. You've learned to deal not just with a single problem, but with power gamers as they come and go.
It's a lot easier to ban or nerf someone that it is to convince someone they are at fault and that they need to change their attitude. But the second away is far more rewarding long term for everyone at the table.
I'd personally suggest telling the player his character is very well built, but the fact that it's so well built makes it hard for the party to play with them before taking through all this and asking if they would be willing to roll a new character. This gives them the chance to build someone they really want to play as rather than a set of statistics they really want to play with.
And I'll finish my dealing with them shpeal by saying its a slow road, his first new character will still probably be a little over the top, but that's ok, let people have a few perks so long as it's a step in the right direction. it will all improve with time and effort, and you should be able to see the work that used to go into making a truly powerful character goes into playing a truly in depth 3D personality.
---
When it comes to other players in the party, who just don't feel they match up to the others, try giving them rewards for roleplaying well and abilities that link to their character, by strengthening all of the less powerful characters to something that balances to that of the stronger players you've created an equal party by helping struggling players rather than punishing successful ones.
It's a lot harder to complain about your ally getting stronger than it is to complain about you getting weaker. I don't know many players who would go 'no I don't want that new cool ability' or 'why are you making our team stronger, that sucks'
Then all you need to do is make the new monsters challenge rating appropriate by buffing them a little and your done