Overclocking was great back when it paid off. Old systems could get as much as 50% increase, these days, the return on investment is so low (after you get better cooling, power supply, case...) it's not really worth the effort. Not to mention an I5 is so far ahead of the software it's not really a concern. Yes, there are cases where a faster CPU helps, but the CPU is rarely a bottleneck these days. Go with an I5, if you can swing a K series go for it, but really, it's not the best place for your money. I would recommend more memory or getting a quieter heatsink/fan combo rather than a K series. You will get more from the silence than you will shaving 1/1000 off boot times. I would also recommend an SSD, if only a 128gig, that's something you can feel, and yo especially if you have a real ultrabook with an SSD. I would start with 8 gigs, but leave room for 8 gigs more.
Since you are not overclocking, a basic board is fine, especially if you plan on getting a sound card later. However, by the time you get a decent sound card and wireless, you could get a higher end board with both of those features included.
Spend whatever you have left on the best video card you can get for $300 or so. Much above that you get less bang for the buck, too far below and you get something that won't last.
If you plan on buying parts a bit at a time, start with case and power supply, those rarely change much. Then motherboard and cpu (wait as long as you can, then buy the best you can, don't wait for the next best thing or you will be perpetually waiting. Ram, ssd's and hard drives are quite volatile and tend to jump around, with the latter two usually only dropping. Traditionally, prices will level off late Novemember, you might see a sale just before or after Christmas but expect prices to go up after New Years and that will last till Spring before prices start falling again. Final note... DDR4 is coming, so DDR3 prices will fall, this can be good for buying now, but also means later upgrades can be more of a hassle. It won't be like DDR2, there was special circumstances (flooding) that caused DDR2 to skyrocket at end of life, but it won't be on every shelf either for much longer.
