The sh3 (133mhz) is clocked a great deal slower than the sh4 (200mhz) used by the dreamcast. The Dreamcast also had a very powerful (and funky) nec pvr2 graphics processor. The Cave games shouldn't use most of the cpu, so it's likely possible to underclock or at the very least idle skip a lot of that. The graphics processor is unknown/undocumented. So i can't really make a guess there as to what it's going to take, but it looks fairly complex (not 3d-hardware complex though). The graphics are almost certainly not 3d, but it seems to be able to do alpha blending, zooming (variable), and it seems capable of loading an assload of sprites onscreen at once.