Normally, I don't recommend dynamic driver IEMs for isolation, as they have to be well-vented for good performance, lest they be microdrivers <6 mm in diameter.
The RE-400 isn't too bad with regard to isolation, but IMHO it can be better. Any deep insertion IEM will best it when it comes to isolation. But yes, the RE-400 has great sound quality.
But my personal inclination is that it's not quite well-built enough for outdoor abuse. Riding in a moving vehicle such as a motorcycle or bicycle, you might accidentally snag on something and moving at that velocity will incur serious force on the earphones. I'll always recommend something less expensive.
Dynamic driver IEMs you can consider:
JVC FXD70 (U-shaped signature)
Yamaha EPH-100
Zero Audio Carbo Tenore
Etymotic MC5
Etymotic EtyKids EK5
Balanced Armature IEMs to consider:
TDK BA200 (if you can find it for the right price, it'll give you the best SQ)
Etymotic HF5
Again, none of these choices are as affordable, nor do they offer any specific concessions for a more secure, sport-oriented fit. The Sony XBA-S65 really is good enough. Read what people have written about the XBA-1 or XBA-10, or even the XBA-C10 (you can even consider that model). They give you a balanced sound signature at decent sound quality, and right now basically come in a a bargain price, especially the XBA-S65. I am not a Sony fanboy, but I do encourage people to take advantage of a good value.