been riding bones spfs for a while know, but im finally wondering about trying formula fours. spfs are just kind of limiting as great as they are at the park. every crack is so jarring, even on a smooth sidewalk.
not only that but the size/shape options are limited for spfs, 54 conicals feel a little clunky, and thats as small as they come. stfs come in more sizes but felt significantly significantly slower at the park.
101a radial slims or tablets sound pretty nice.
I have SPF, STF 103, STF 99, F4 101 and F4 99. At the park, SPF are fastest - but my STFs are not far behind. I'm not sure why your STFs felt significantly slower. Were they the same bearings? Next, I find 101a F4 and 99a STF to be about the same speed at my super smooth park. Slightly slower than 103 STF, but acceptable. 99 F4 to be the slowest of the bunch - and the only ones I find are too slow to ride there.
On the street, 99a STF and F4 are better. 101 F4s aren't too bad - much better than SPFs.
For me right now, if I had to have one setup only it would be 99a STF in a 54mm V5 and ceramic bearings.
But instead I have 8-9 setups, because i have problems.