The RGB is the way to go if you want MX keycaps on a Topre board. Older Realforce keyboards didn't have a standard bottom row, but the RGB does, along with all other R2 models. The last I checked, it was difficult to make the space bar compatible with an MX type using aftermarket sliders. The RGB has no issues with that, either. The RGB is also typically the cheapest way to get a uniform 45g Topre, and they sell for less on eBay than other models because of a misconception that they're someone worse than other Realforce keyboards. I've owned both, and it's just not true.