The CSi is a splendid car. A mix of competence, comfort, speed... and an unshakable feeling of specialness, coolnes and again competence. It can do almost anything for every occation. My friend have two 850's, one Ci and then the CSi. The CSi is an animal compared to the Ci. You can cruise around, then shift down the 6 speed manual gearbox and just GO - with more speed it just seem to bring more acceleration. It is just great.
His car is modified with a special exhaust, the noise is "from heaven", the springs are Eibach and with Bilstein dampers, and BBS racing wheels it makes for an even more special car. As I'm sure your CSi is as well
The car is a KEEPER
About the 911. Have you tried out various cars? An SC, a 3,2 Carrera or an early car? They are very different. The Turbo, especially the 964 Turbo is also a wide and not exactly lightweight car. Maybe a lighter more nimble 911 would make a bigger "contrast" to the CSi? And also be cheaper and make it easier to keep two enthusiast cars?
A 964 Turbo is like the CSi also a luxurious car, "silent", competent and with much comfort. An SC or earlier car feels very different to drive, and is much more alive and kicking at "sensible" speed.
Another friend of mine had a 964 Carrera 2 and later a 964 Turbo. The Turbo was a great car, but I think like the CSi it felt a bit like an Autobahn-Crusher and better the bigger the speed. The engine of course it awesome, but the turbo quietens the exhaust and the on-boost-torque dominates the experience. Overtaking is easy and power and torque massive, but that is the same with the CSi. An example - to play music on the stereo in the C2 and in the Turbo is very different. In the C2 the stereo had to compete with the "noises from the car, engine and the roar from the tyres etc". The Turbo is a much quieter car so playing the stereo is more "rewarding".
Don't misunderstand what I am trying to put down in words here. I have driven several 911's from the earliest to the later ones. All are wonderful, wonderful cars, but they are oh so different. My heart beats more the older the car. I guess there are many here that share that wiew
What I am thinking is that an older-simpler-lighter 911 might make a nice companion to the CSi. I guess I'm trying to say that I think you would bitterly regret selling the CSi, and that byuing a Turbo might make selling it a tempting possibility.
An older 911 would not do that. It is a much more raw and unpolished thing. I guess it means that I would get a torsion-bar era car, possibly an SC. This is a raw car, with little in creature comforts, you need to really use force to steer it and to brake and shift. The more you involve, the bigger the reward in the drive. It is not so much about raw speed, but more about the way the car speaks to you and communicates with you. Like Magnus Walker so nicely says about the older cars. Magnus also owns an older Turbo, by the way!