ChipFlip
The Core i9-9900K costs $85 more than the Core i7-9700F used, $179.99 against $94.99. Both launched the same year, both share the same generation of Intel architecture. The 9900K adds hyperthreading and an unlocked multiplier the 9700F doesn't have. Is that worth nearly double the price?
What hyperthreading actually adds here
The 9700F runs eight physical cores with no hyperthreading, eight threads total. The 9900K runs the same eight cores but adds hyperthreading, sixteen threads total. For heavily multi-threaded work like video encoding or running several demanding applications at once, that doubling of threads shows up as a real, measurable gain. For gaming, where most titles still lean on a handful of fast cores, the difference is much smaller.
The 9700F has no integrated graphics, and that matters
The F suffix means no integrated GPU, so this chip requires a discrete graphics card to display anything at all. That's not a downside for anyone already planning to run a dedicated GPU, which describes most builds this chip goes into. It's worth flagging anyway, since it's an easy detail to miss on a used listing.
Where the extra $85 makes sense
Content creation, streaming while gaming, or any workload that benefits from more available threads. The unlocked multiplier on the 9900K also opens the door to overclocking, something the 9700F's locked multiplier doesn't allow.
Where it doesn't
Pure gaming builds on a budget. The 9700F handles gaming nearly as well as the 9900K in most titles, at close to half the price. If overclocking and heavy multi-threading aren't part of the plan, that $85 buys very little you'll actually notice.
Bottom line
Know your workload before paying the premium. Gaming-only build, save the money on the 9700F. Anything leaning on heavy multi-threading or overclocking headroom, the 9900K earns its price.