With my setup (Smarty + Mach 1. 6 + HX35), I pretty much tow by the pyro. Not that EGTs are hard to control, I'm just a compulsive gauge watcher when towing and a smoke control nanny when empty. Most of my driving is empty and I often wish I'd just gone to M4s and been done with it. Then I wouldn't feel like I still had an injector step to go. Most of my upgrades have been small increases, satisfying but not exciting. The possible exception was the Edge Comp, which I couldn't fully utilitize without burning down the house anyway.
My turbo selection is hamstrung by my elbow mounted exhaust brake. Your inline brake makes turbo upgrading a much less painful proposition. There are so many turbo variables that you're better off getting your fueling and driving style in order, then buying a turbo that fits your needs.
Maybe the M3. 5s will be too good a deal to pass up
