Hi, many of those questions can be found by searching the board!
Exclusive private IPs are usually hosted on datacenter servers while DSL is a home connection.
So the difference is speed, ability to change the IP on the fly, ability to change to a specific IP instead of a random one and DSL is shared while exclusive IPs are not meant to be shared.
And this is where the troubles begins, you can be lucky or unlucky using DSL. Craigslist always looks at IP addresses as /24 net (x.x.x.*), if they mark a subnet as spammy you will have troubles and it might risk the PVA.
It depends how large the IP pool is and how many people advertise on CL in your pool.
The same can happen with exclusive proxies, depending on where you buy them (you might want to checkout my seo-proxies.comhttp://www.blackhatworld.com/blackhat-seo/proxies-sale/107493-new-exclusive-http-proxy-service-api-multiple-subnets-auto-browser-configuration.html for clean exclusive IPs) .
If you have no troubles with resetting your modem, ghosting, PVA loss or geo blocking you should consider to keep your setup as it is. Private proxies cost money and if your home connection works for you .. why invest more ?
To tell if a proxy is shared or not is hard, often impossible.
Some IPs can be judged by looking at them, check their reverse DNS and it might already give you a clue.
After all you need to trust the proxy provider and know what the service is about.