It is old in terms of age (6.5 years), but not old in terms of relative performance to what's out now.  Don't worry about the age of your stuff except if you think it will cease to function.  Intel warranty is based on a mission critical 3yr used 24/7, if you use it less than 8hr/day, it will certainly last longer-- except there are other components in your system with different lifespans.  So take heed of them.

The deal with relative performance is that Intel's hasn't been bumping up the IPC (instructions per clock) that much over the years, mainly due to competition (AMD) not even trying.  On average of CPU-bound apps, the Core i7-4000 series is about 30% faster per clock, which means at the same frequency/overclock as your i7-920, you gain a 30% advantage.  That is all that the last 6 years have give us.

Whether you think that gain is worth dropping a minimum of $500 just to get the new CPU, mobo and RAM is up to you.  
Intel has been compensating for the abysmal IPC by raising the stock speed clock.  So while Haswell is 30% ahead of Nehalem, the top model (i7-4790K) at 4GHz adds 50% more on top of something running at 2.66GHz.  So if you upgraded to i7-4790K, it will perform 80% faster than a stock i7-920.  Most new quads nowadays can overclock to the middle 4GHz range (pushing relative performance even higher to 100% ahead of an i7-920), and some folks attribute the higher overclock as worth it over an older CPU that did not overclock well.

But I don't like to gamble on overclocking potential because it is based on the silicon lottery (i.e. random luck); and my i7-920 wasn't stable past 3.7GHz.  

I agree with the X58 still being a good platform for gaming rigs and even for production as well.  Like many have said the Xeons are for the most part the way to go.  Most of the top end Xeons are no more than $200 for six cores.  Just keep in mind if OC'ing is a factor in your choice of a new CPU then keep in mind many(if not all) retail/non-ES Xeons are locked on the multipliers so they are only overclockable via base clock.  Look for a CPU that starts in the 3ghz+ range, whether quad or six core.  IIRC I picked up a Xeon X5590 for like 60-80 bucks which was the top tier quad core Xeon.  Six cores can start as low as $45 for a low 2ghz model but keep in mind you will barely hit 3ghz only using bclock to over clock them(if you are lucky).  Maybe it's just the SR-2 that was prone to this but from what I have seen and heard 200 on the base clock is about the limit and stock is 133 so do the math and look for a reasonable clock speed for your processor that can be reached in the 160-180 base clock range when looking at Xeons.
 
Honestly if you are gaming at 1080p the X58 will serve you well.  I say this because pushing surround or higher resolutions of course requires higher end cards.  While for the most part PCIe 2.0 does not hold FPS down on newer cards it is the limiting factor(however small it is) when it comes to GPUs on the X58.  Cores/threads are not much of a factor in gaming yet compared to clock speed, and quad channel has not proved much of a boost.  The same for DDR4 for the most part in regards to gaming.  X58 is the sweet spot as it has everything you need for quality 1080p gaming.