Hi Gnana,
OK, both amps will work fantastic with your speakers, no question....As for the differences of the amps, well, the Kismet has been so upgraded and changed, that it is not really a SL anymore, even though it surely has that family sound to it. With the SL RG 1, a Mk3 has been in the late 90's, but there is a difference between Sanken and Toshiba's (in the earlier Mk3's) on the output side. The Toshibas are not made anymore, and that is a huge problem if something goes wrong...Ultimately, considering the price difference, I would suggest the Kismet for you, especially at this attractive price. It's quite close in performance, and if you'd have a problem down the road, I'll help you out personally.....
Now, as for a Mk4 amplifier, that would be easy to service, but man, you're talking a completely different price point here. And as for the RG 4's, they are ridiculously good. If you have that kind of money to spend, then definitely go with it.........
Hope that all helps. Bottom line, look at your budget, because you only have great options here.....
Late,
Klaus