Oh dear. More detail please. What is "frame rate suffers"? How many fps are we talking?

System specs could help.

Frame rates are influenced by a number of things. your system is only as fast as the slowest component. Find the bottleneck and fix it, by looking at performance charts, cpu/ram usage, determine when frame rates are slower. Are you loading things slowly? - hard drive, possibly. Do things run fine and then suddenly go kerplunk? Maybe you're using all your RAM and are using the paging file, which is on the HDD, which is a slow part.

No, SSDs do not undo the advantage, unless you have so much ram you can create a RAMdisk to house your wow folder, which would be expensive and unnecessary unless you happen to already have enough RAM.