Are LGA775s going to be around much longer?
Doesnt matter and here is why. And I know because its happened to me virtually every time I've bought a machine or built one
Lets say you build a hot rod system using the latest motherboard with an eye on not having to rebuild the entire thing in the future.
Whats going to happen. Is by the time your ready to get or build that next machine. That mother board. and most of the parts are going to be old school already
that LGA 1336 (for example) will be replaced by QFT 4,000,000 And quad core CPU will be replaced by some triple quadruple quad with a mind meld co proccesser, Your PCI card wont fit the new slot designed to take video bricks that will look more like a circuit breaker and will plug in pretty much the same way.
Forget that old PSU. the micro mini nuclear 450 gigawatt reactor PSU will be needed to power it all. And a turbine wind machine to cool it all
Point is. Get what you think will last you a few years. Then just start saving for a new build.
6 months from now anything "new" you get will already be old technology.
After 4-5 years the money you saved by not buying upgrades will enable you to build a completely new machine and start all over again
That being said. A really nice machine can be built with a $1,000 hard price limit