Dirt Rider Magazine

To be honest, either. Unless you are going to dyno each pipe and see what they do in terms of specific RWHP and torque, either will work fine. Now, some pipes do differing things in terms of adding low end power or top end power, but the smaller the engine, the less options you have if memory serves. What are you looking to do?

The real question is how old are you and are you planning on getting a bigger bike later? If you are young and still moving up in bike size, I would not worry about adding new parts to increase power all that much right now. Unless you race in a truly competative way, and even then I would not worry as much until I hit the 125 2t or higher. Just my $0.02 here.

IMO getting the engine ported is the most cost efficient way of modifying/enhancing the power band of a 2 stroke.
http://www.eric-gorr.com/ can get you  as much of what you want as possible.
Because of the small bore of an 85 it is hard to get a lot on the low end these things need to rev to really make power.

If you are set on a pipe.  My experience is
PC tends to be a bit harder hitting and freer revving very good for tacky moto dirt can be a bit much for slick conditions or an inexperienced rider
FMF typically provides a bit smoother powerband it is really good for multi purpose riding (track and trail)
The Fatty is a great do it all in all conditions pipe.
The SST tends to get a bit more on top and is a very good motopipe not quite the hit of a PC

both PC and FMF are good just depends on type of riding, style, terrain experience of the rider...IMO most newer riders do better with an FMF Fatty.
One last comment because of the process for making these pipes no two will perform exactly the same,

Mark,

You know Eric Gorr is shutting down and going in with Millenium, right? Yep. Check out Gorr's site for the info. They may have already closed the doors.

I could not remember when he was closing his doors. I knew it was due to a higher volume than he could handle these days, and after several years of doing it. But I also know he is getting all but his own section at MIL. That is sweet.

Skyline I notice you are asking numerous questions about how to make your bike faster,

Here is the most effective performance gain you can get.  Riders such as McGrath, Dowd, Windham Villipoto just to name a few have invested personal money into this upgrade to make there bike go faster  http://www.gsmxs.com/