Have not installed them on the car with fluid running to them to test feel, however based on calculations for pedal torque, travel and BMC size, I expect the following (if you were to control for lines/fluid/pad type):
OEM pedal travel is pretty long stock, so the WRX 1" or STI 1 1/16" mc are both a good upgrade with stock brakes. It's not required for the 17Z calipers, but definitely a worthwhile change, especially with a STI booster.
Using the 17Z calipers & LGT rear sliding calipers, there is only about a 5% increase in pad area. Using the 17Z calipers and STI rear brembos, reduces this to about 1% (STI rear brembo has a smaller piston area), but shifts the bias forward due to increased front torque (73.9% to 75% front, OEM is 72.2%). This could be balanced by having a more aggressive rear pad, however with how nose heavy our cars are, its likely a good thing, or at least has minimal impact for 99% of drivers.
The pedal travel will be about 5% longer with the 17Z calipers and OEM LGT master cylinder (15/16"). The STI master reduces travel by about 18% with the 17Z calipers, compared to stock MC/brakes.
As for banjos, normally I would caution against them as there is nothing to prevent the line from rotating and loosening the banjo (Audi/VW people have leaking issues when using banjo lines instead of male flare fittings).
However I took a look at my test set up, and a simple p-clamp to the upper caliper bolt could remove this risk. The OEM LGT M10x1.0 banjo bolt fits the 17Z caliper, so this could be a cheap, simple solution that avoids custom lines. Photos show an LGT OEM line and OEM banjo bolt attached to the caliper.