solid are something for racing only, and I mean it. I had solid aluminum engine mount for my 4AG-E pwered old MR2, and made it ride like horse drawn buggy...
ok to elaborate on that... the solids are much better as far as preformance goes, takes away some of the driveline losses.. but your car will vibrate (the engine cant move in its spot so it moves the whole car.. if you can deal with the shaking(wich isnt really that bad) then go for it, it personally dosnt bother me, so id go with the solids..
now alot of people have diffrent thoughts about what is for street and what is for race, or maybe around here we are just crazy... stroked 351(393) witha raunchy cam and a carb in a fox with solid mounts is considered a street car around here
the way i see it, no matter how insane my car gets, i'm going to drive it at least a couple days a week, i didnt buy the damn thing to be a paperweight.. and i'll do anything that makes it faster, if that means having to deal with the vibrations, so be it, but solid mounts are better for the preformance.