Again, I would never suggest upgrading from a 3770k build as the performance difference is negligible. As i said both times, performance is not in the evaluation equation.
I have a 2600k, twin 560 Ti build that is till going strong and see no reason to replace it.... I wouldn't invest in any of those parts today tho. If MoBo / CPU died, I'd move to a new MoBo / CPU combo rather than invest time, effort and money in replacing either..
However performance between 3770k and current CPUs can range from negligible to 100% or so depending in the game and whether we're talking IGP, AMD or nVidia cards
On Grid AutoSport, 1080p per anadtech performance goes from / to ....
min fps frpm 14 to 28 fps on IGP
avg fps from 81 to 109 fps on 290x
However, from a financial investment standpoint, it's just hard to justify. Look at any review for a new MoBo generation ... the difference say between Z87 and Z97 and invariably they will state that 1) If you have a Z87, there is no reason to upgrade .... but 2) if you are buying today, they invariably recommend going with the newer technology....and that's when the technology is still current. Not after reaching EoL.
Have you ever tried getting TS from Asus when not original owner and no original receipt ? I gotta wonder about the "two months" thing as I haven't seen Z77 boards on the major sites for quite some time. Who was stocking Z77 boards and 3770ks 2 months ago ?
The 3770k is 3.5 years old.
How many Z77 boards can you find on newegg ? One... an Asrock and an open box Asrock same model. So if the MoBo dies, what are your options ?
-Buy the Asrock and a new copy of Windows.
-Try and find an identical MoBo on ebay and deal with the risks associated therewith.
-Buy a new MoBo, new CPU and new OS
As photonboy said, I'd wanna see the original receipt; MoBo manufacturers have to provide replacements but they do NOT have to be exact same model. I have had top tier GFX cards replaced with new generation 3rd tier models which offered equal performance. I had an 1156 board replaced with an 1155 board; they didn't pay for the required new CPU tho.
That model board is 3.5 years old and it was made for about a year. So at best, it has 6 months of warranty coverage left in it unless you have an original purchase receipt in your name. Even then, Asus may not honor it if you re not the original owner and the manufacturing date is 3 years old.
$300 seems attractive as compared to $500 ($450 actually) but not if you wind up spending that $450 anyway + a new copy of Windows, 6 months from now. I just retired a 2600k build and wouldn't have the heart to charge someone for it. I kept the HD, DVD and GFX card and gave away case , MoBo, CPU, Cooler for half a pizza. I brought over the stuff to his house, we installed his GPU and accessories, and I got free dinner. That's about what I felt it was worth. For a 3770k, I would asked for a Corona on top of the pizza

All kidding aside, paying 2/3 of current generation equivalent costs for 3.5 year old technology is a good deal only for the seller.