I thought you would never ask!
Such a massive subject but to summarise. Any K chip is unlocked which means it can be safely overclocked.
Get a board that has over clocking as one of its features, this will ensure a minimum user error (less chance of blowing a chip) its not like the olden days when you just pushed it until it got to hot or popped these days board manufacturers build with it in mind. water cooling will allow you to overclock higher with minimum risk.
get a board and chip combo that is well supported to help you in clocking.
I like ASUS boards and Gigabyte, Gigabyte boards allow you to run OSX out of the box so if your in to CAD its a very good way to get a MAC on a very nice budget
16GB Ram is ample for most high end CAD users.
I would get this: Gigabyte Review
here is a good Overclocking guide for it
is where you can buy it.
one last thing, if you fancy a go at building a hackintosh have a look HERE
OH! and one final thing (teehee) if you would like a pre built computer saving you some cash in the process let me know as I have an ASUS board with an i5 3330 for Sale