I now run a continuous piece of housing from the top tube cable stop near the seat post all the way to the rear dérailleur. The great benefit is that mud and gritty water is much less likely to get into the cable housing and gum up the shifting. Most cross bikes route the rear mech cable along the top tube and down the seat stay. This means that gravity greatly assists water (and grit and mud) to travel down the cable and into the housing. Running a continuous piece of housing down the seat stay protects the cable and housing from much contamination.
I’ve used zip ties to attach the housing to the seat stays but some folks will drill the stops and run the housing through them. The long piece of housing wants to deflect under load and that can result in mushy shifting. Therefore, I recommend at least five very snug zip ties to attach the housing and if you drill the stops, I suggest that you supplement them with a couple more zip ties.
Here’s a picture of Andy Askren’s Speedvagen that was built for continuous housing. In the two following photos, you’ll notice that there are four routing points plus the top tube cable stop. I’m guessing that Sasha did this to keep housing play to a minimum.
The shifting on my A bike is still acceptable after an incredibly muddy race this past weekend. I’d bet that there are a bunch of other guys changing out there cables this week. Not me.