Both Fostex and Lowther are good drivers. Some will prefer the Fostex, and some will prefer the Lowther.
Personally, I found the Lowther drivers to be what I preferred.
Generally the Fostex drivers are a little bit less in sensitivity, with about 94db being typical for them, whereas the Lowther drivers have models going up to 99.5db sensitivity. This may be useful if the amp's power levels are quite low. The Fostex will be just fine with anything about 8 wpc and over.
I think that the Lowther has more detail and is a bit faster and more transparent, but they cost alot more than the Fostex.
There are proponents of both brands, and ultimately you would have to decide which you like, and which suits your budget and system best.
I'd like to add that the 1.3 bass-reflex box for the PM2C is not really the right design for Lowther drivers. The Lowther is designed to have the rear-wave loaded into a back-horn type enclosure, or a Voigt Pipe(Cain&Cain Abbey type).
Also, the PM2C is the "budget" Lowther, and has lower sensitivity around the same level as the Fostex, has ceramic magnets, and offers less detail, speed, and transparency than the higher Lowther models. But they are still good speakers. They would be probably more similar to the performance of the Fostex models.