Shikari, I only wish I could afford a rising bite, that is my dream rifle. That and a Holland & Holland Royal in 500/450 like Teddy's Big Stick! In the past I tried to buy a couple of rising bites but I get out bid. I have a long length of pull, 15-1/4", and I find a lot of the older rifles both from Rigby and H&H have shorter length of pulls. I found a beautiful H&H Royal from 1917 in 500/465 that was in great condition and I was going to be able to acquire it for a very good price but alas it had a 14-1/2" length of pull and there was no good solution to fix that without detracting from the value of the rifle so I passed.
I also wondered why the 500 recoil felt less and Jerome said it is because better fitting rifle and the fact that the 500 weighed about 1 lb more than my 470. The felt recoil was definitely less to me.
For me the recoil is only an issue when I am practicing. I used lead sled for sighting in my doubles, I follow the instructions and advice from Graeme Wright's 3rd addition of Shooting the British Double. And with the extra adrenaline when shooting at game in the field I do not notice the recoil. So when I practice, generally off sticks and some free hand, I shoot about 10 rounds and then take a break for an hour or more and then shoot another 10. This way I don't develop a flinch.