I have Siri and it seems strong to me. It's also SUPER quiet! I think you'll be happy with it. But you might want to consider mimi or something since it's waterproof and I hear it's also strong and very quiet.
I have heard the siri is stronger. Though I agree, if you need really strong, Lelo may not do it for you (I know...they are so cute!), maybe you should look into Salsa or Tango.
Hun, neither one of those is a good strong vibrator. Look at mimi, or the wevibe tango for a strong discreet clit vibe. If you feel you must have lelo, mia is a 3 vroom toy that some women like, but it wont be as strong as mimi.