Maximus IX for gaming/performance/overclocking.
Apex is the oddball model. The choice for "record-breaking" maximum overclocking "at any cost", but it streamlines away other (important or useful) features and functions.
Extreme is the best model overall. A very strong overclocker with full motherboard functions and all the ROG features which enhance gaming.
Code is the best aircooled model. A strong overclocker with full motherboard functions and almost all the ROG features which enhance gaming.
Rampage VI for computing/overclocking.
Apex is again the oddball, built for maximum overclocking at the cost of sacrificing other things.
Extreme is again the best model overall, a good overclocker packed with full functionality and features.
Z270 mobos and LGA1151 CPUs run faster clocks (and overclocks) than any other Intel part. Fewer cores/threads and caches and lanes, but still easily capable of heavy gaming. Many i7-7700K CPUs can run stable overclocks >5.0GHz with adequate cooling (and de-lidding, lol), alongside extreme DDR4 speeds.
X299 mobos and LGA2066 CPUs run fairly fast clocks (and overclocks) but offer more cores/threads and caches and lanes, built for computing multithreaded madness.
The "X" in "Core i7-X" meant "Extreme" - biggest, baddest, best, fully unlocked.
The "X" in "Core i9-X" basically means "Xeon" - call it "Core i9-Xeon" - although with lesser specs and fewer technologies than a proper Enterprise-grade Xeon.
A big bad HEDT system is great at running multiple instances of multiple things, running many VMs, computing more complex tasks in parallel, being a fileserver for dozens of simultaneously-logged-on users, etc. It's built for boring reliable server types of stuff, high-density computing with maximum proven reliability and unexciting (but generally adequate) performance.
X299 vs Z270 is sort of like comparing a powerful Hummer vs a speedy Lamborghini. The bigger engine can haul more heavy data across harder computing terrain, but the faster engine wins the race every time when running smoothly-paved games.
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