The Subaru short shifter, which is the STi unit, does decrease the throw noticeably although I can't tell you how much in percent or whatever. You will notice the difference. It is one of the most expensive options however, you can also consider the Kartboy as well as other similar ones that are much less expensive and only replace the lever rather than the whole linkage. If you have decided on the Subaru shifter (which I'm not knocking BTW, I have it on my car) you can shop around for the best price online instead of just going to your dealer. It is something you can install yourself if you have the knowledge and tools, not all that hard, although the lever-only ones are much easier because you don't need to work under the car.
Also note that a short shifter isn't necessarily going to allow you to shift faster, it will just reduce the throw and improve the feel. How fast you can shift is dependent on other things such as the transmission itself and how the synchros work, and even with a short shifter you still have to allow time for the gears to synchronize, you can't just slam it from gear to gear.
The feel and tightness of the shifter can be improved even further, regardless of what shifter you have (even stock) by replacing the bushings in the shifter support rod with the harder Kartboy ones. This is one of the most inexpensive yet cost-effective mods you can do and is definitely a DIY- although the bushings are under the car the actual install isn't difficult.
As for *****- yes the Prodrive is easier to install as it uses the same retention system as the stock ****, but the universal set-screw types like the Momo are fine as well. You just have to install them properly and make sure the screws are evenly set and tightened, and you also need to come up with a way to keep the boot up under the ****, also not that difficult. Another alternative if you decide on a Momo **** is to contact NASIOC member "Paulie" (he may be on here as well), he makes inserts for the Momo ***** that convert them to the same mounting system as stock.

FYI, my setup- STi shifter, Kartboy bushings, Isotta (Momo-like) **** (fake carbon fiber, anatomical shape). Aside from the feel of this ****, I like it because it is thermally neutral. Metal ***** tend to get very hot in summer and very cold in winter. This one doesn't. Oh, the Momo collar is from another **** just for show.

 

thanks Mulder, your message is a huge help. I am thinking of doing the shifter mod myself and was wondering if the shifter bushings were all that helpful.