Quick glance reveals these run at around 12MHz, which may be a bit on the slow end for algo trading (?)

I mean, Algo traders I know are working on teams of 10-20 people with deep knowledge of $5k boards over a half-decade, so I think for "getting started" those might be pretty good.

If you have the v2 board you can use the PLL to change that 12MHz up to a high frequency (150 Mhz maybe?). You have to use a block and the icepll tool will generate the code for the frequency you want.

iCE40 ICs have both 10kHz and 48MHz oscillators built-in, as well as multiply/divide capable PLLs that work up to 250 MHz.