"Speed" Skates

I'm feeling tempted to drop the annual birthday cash on a pair of speed skates because I'm interested in doing longer, more athletic skates and advancing my form. Only thing, I'm fairly speed shy even on the PS Nexts (3x100) that I have now. I'm not confident enough in my powerslide or stepping plow to really push, and I've never gotten my thighs into that anaerobic burn I know well from biking and running. So is it dumb to get to invest in speed skates? If I want to work on form (double push, core engagement, etc) and skate marathon length routes, should I just do so in the Nexts? Maybe upgrade the frames to 4x100?