The RX-1's are definitely narrower than the Nuevos and made with weight savings in mind. that means in part that the rear plate is held by 3 screws instead of four, and the front by only two. If you hit a pedal, you are more likely going to have to replace the pedal because only one bolt needs to get bunged up. You can get RX-1's in gold as well, if it matters.

The Nuevos are equivalent except for bearings and the color of the plates. They are wider than RX-1's and a bit beefier. For some reason the dust caps tend to come off a little more readily than on the RX-1s, but they are easily and inexpensively replaced if that happens.

Are you planning to use cleats? MKS is converting their pedals to work with a relatively new slotted cleat that's really great. It has a deep slot and fits 3-hole Look-pattern drilling on cycling shoes. It already fit the RX-1 (which didn't have to be changed). If you're buying pedals right now, the Nuevos are in production but still getting NJS certification (the distance between the plates had to be changed slightly) so you can't get the compatible pedals (I've also heard that MKS just wants to sell their existing stock before making the new pedals available). The new ones will replace the current versions once they are available.

As for the Sylvans, you get what you pay for, but they definitely aren't RX-1's or Nuevos. Poorer metal, poorer finish, bearing seats aren't machined as well so the bearings (which may be the same as in the other pedals) don't seat as accurately and feel like they're binding or clicking a bit. (The cost of sealed bearings is in the bearing seats, not in the bearings -- it costs money to machine the aluminum to high tolerances and to do the same to the steel axles where they fit against the bearings). Personally I'd go for RX-1's right now if I had to buy immediately. If I could wait three months, I'd have more choices available.

Edit: As for fitting double toe straps, you can do it with RX-1's. This is an issue many pedals have, including C-Record, Dura Ace PD-7400, and the like. You don't really want to put a strap in the front pair of holes in a Nuevo anyway, because it's too far forward to do much good for most people. Instead, most trackies run one strap in through the slot on the back of the pedal, around the center vertical strut on the back plate, and then back out the other slot on the other side of the strut. Then run the other strap straight through. You can also do it a bit more elegantly by running one strap in through the outside slot and the other strap through the outside hole in the frame, then cross them under the pedal so that the front strap is now in back, and vice versa. What started as the front strap then comes out the inside slot on the rear plate of the pedal, the erstwhile rear strap now comes out the strap hole on the inside of the frame, and then both go up and over and into the buckles. The original rear strap tip goes into the front buckle, the original front strap tip goes into the rear buckle. Looks nice, works well.