Yeah the KG3.5's are bigger than the RB-81. Like I said it is a better bang for the buck. When you buy RB-81 for some $799 (or $699) you also need to get stands. Like I have also said before, there is no cheap stand in the market now that will be a good match for the RB-81. The partsexpress high mass metal stands are the ones I used and they are discontinued. Other cheap stands are flimsy with a small top plate. They are just useless. You are better of doing DIY stands using MDF.
KG3.5's come with spikes (yes not just plastic feet) and for under $200 you get a much better performance.
To me the KG's are reference grade. They sound better than RF-82. RB-81, PSB Image T-65, all of which I have owned. Heck they even have the similar sweet highs like my Magnepan MG12 (both compared after applying either manual EQ or Audyssey) and not to mention the tight bass.
People dismiss that they sound better because those speakers are old and also they have spent more money on new/current models, no offense. That is your right. I have tried many speakers (mostly new current models) and never been as impressed by the KG's, especially for the money I spent. I bought a pair of KG3.5, KG4.2 and KG 4.5 (all in great shape) for a total of $618 (including any shipping). I bought the Klipsch RF-82 brand new for $768 (got a deal at 6ave) and sold it for $540 (very very low hours, basically brand new). No I didnt hide what I paid for RF-82. I gave the buyer the original receipt.
I also got a pair of KG2.5's at local CL for $70! Got a single KG3 for $132, spent a few bucks to sand it and restain it. I might sell the 2.5 for more and recover some money I lost with the smelly KG4.2. A pair of 2.5's got sold on eBay for over $200 last week!
The only thing where I thought I got burned a bit was another pair of KG4.2. Paid $242 shipped from eBay but it had a strong smell which the seller didnt disclose. I was able to get rid of the smell from one, which I am using as a center. I am not able to completely get rid of the smell from the other KG4.2. It smells like cigarette may be, if I put my nose on the front or rear plate? I am going to remove the drivers and crossover and sell them separately or make an attempt on DIY cabinet just for the experience.
That is my Kg story