Well let me say this before anything.... I'm not an expert, nor am I trying to convince anyone I have all the answers. I'm too lazy to search notes that may or may not still be in my garage, or that may have fluids spilled on them. What I can tell you, as many members already know, I'm a cheap bastard, but I almost never skimp on quality, when it comes to my toys. It's a toy, and the "disposable household income" is usually quite lean. If I buy it, I can't risk buying something that "could" do what I want, for a lesser price, over a known quality product. I wear many people (experts) out via phone, asking questions before a big purchase. IMO everyone should too.
My understanding - the fgk is cartridge kit, install in OEM forks.
fgr is the entire fork assembly.
One of the differences between them is the titanium nitride coating on the stanchions of the rt. Opinions are widespread, but many I've talked with claim the GenPop will never feel shorted running carts over the rt where the chrome vs. TiNitride is concerned.
The seals, and a few other parts are likely not identical, BUT you can still add that (seals -low stiction Green SKF, and if inclined, coating DLC or TiNitride).
I added the green seals, due to an article by Kevin Cameron some time back explaining in detail how they were truly effective.
The original 30mm NIX cartridge kit wasn't that fantastic for the s1000rr, and at some point they updated it. In fact Ohlins USA (think it was Brad) told me that Aaron Yates preferred the 30mm kit on the s1000rr over the 25mm kit, whereas Steve Rapp his teammate preferred the pressurized 25mm kit.
Grain of salt, and all that....