Imho only downside to T66-F - cost. Then again, almost all forged wheels cost fortune. All listed can be used for track & DD. Real "track" wheels .. you meant those TWS wheels that have single center bolt mount for use on some track-only cars? Think of it like that track wheel designing know-how/experience of making wheel strong enough but light as possible just has been applied to these wheels that can be used on street cars
Effect of lighter wheels imho is well summarized in eg.
this post.
"It appears that lower unsprung mass (like lighter wheels) results in a less bumpy ride over poor roads. However, the downside is that it could increase the "fine vibrations" that you feel over some "relatively smooth surfaces" such as concrete roads or an asphalt road with gravels."
They can provide a bit better acceleration & grip (but possibly not very measurable by easily placebo affected imprecise butt dyno measurements), due less rotational mass for first and due tire staying with road more of time, but that may more show up in slightly better laptimes, not feel.
I had somewhat similar drop in mass (OEM>Taneisya (TWS is "subbrand of them) T6 (one of their old forged wheels) wheels of 6.2kg). Car felt different. Hard to describe in words .. i liked a bit better ride on bad roads, and it felt a bit livelyier/lighter in acceleration .. but then again i'm not very confident how much is what i actually felt and how much came from "expectation of change". Different tires usually change feel much more in handling/grip.