sorry - I'm - not petite but thought I'd give you that "honest" answer you were looking for anyway........

I'm 5'10 and was recently fitted on a WSD w/ 650 wheels. Before that I had 700 wheels - and to be honest I don't think switching has made any difference. Here are my thoughts on the things you mention:

1) the ride actually seems smoother - but this is probably due to the fact that I now have a carbon seat stay and fork.

2) speed? hmmm, I haven't noticed any problem with maintaining higher speeds - but then again - I don't race - so being speedy isn't something I strive for. I like staying in the 15-20 mph range on the flats and haven't had any problems doing so.

Best of luck!