My personal rule of thumb[0] is modern HSTs (280~320km/h top speed) are superior to plane up to ~1000km, and can remain competitive to 1500km.
(although, though that's much more of a personal advantage, having really shitty ears and great difficulty with pressure equalization the odd train tunnel — even at high speed — is much less painful than going from 0 to 30k ft and back)
[0] modulo specific settings, including the current security theater shit which I don't have to experience on train and considering that most of my experience is on european lines where city center to city center is what you want and airports are commonly 30~40mn away from city center
The only things I'd really change are the price ($48 round-trip is a bit steep as a college student) and the lack of wi-fi. The vast majority of commuting professionals have cellular modems though.
It's really great to be able to move between cities in reasonable time without owning a car, buying gas and insurance, or trying to find somewhere to park for less than the price of a firstborn son anywhere useful in Chicago.
I've pulled out my iPhone speedometer app on the train and it clocks at around 80 in the middle of nowhere, 65ish in the northern Chicago suburbs.
EDIT: Correction, I took the commuter train from Sol to Chamartín, so I do not actually know if there are security checks at the commuter trains at Atocha. But I assume not since it would not scale and there were no checks at the other stations.
They run their tracks right next to each other, so trains are designed to not suffer major pressure changes from passing trains or tunnels.
I write this as someone who has had two cancellations and 6 delays over ten air trips in the past three months.