Johannes, buy a KingAir!
Now seriously, from what I hear, part availability starts to be a problem.
I have extensive KingAir experience and just a little bit of Cheyenne time - in the II - but a near relative of mine flew the II from 74 to 1990 and this bird is reliable. I asked for a memory check and the SAS was inop only once in about 7000hrs in 4 different II´s flown.
Bear in mind that the airplane were new then and are old now (when did production of the II cease? mid eighties?)
Try to contact Aerodienst in Nürnberg, Mr.Horneber. They were our maintenance shop for more than 20 years and have real knowledge of both, KingAir and Cheyenne. Also Jet Aviation Kassel do know the Cheyenne inside out.
Flying the II is big fun, but the Airplane can bite - SE low speed can really give you a handful - hence the SAS. The IA is a good airplane to, the tradeoff in performance is not so big, but it is definetely cheaper to operate.
The II and IA are true `pilot aeroplanes`and a big step up from the seneca.