Sorry for the delay, I missed this thread.
Im simplistic terms, the key differences with the 4000 series automotive scope and the 3000 series scope are as follows:-
The 4000 Series Scope's have a 100V input range, making the use of the attenuator far less than the 3000
Series Scope that has a 50V input range i.e. basic injector voltage tests of between 60 - 80 volts. This makes hardware selection and connection times far less overall.
The 4000 Series Scope has more internal memory than the 3000 Series Scope, this now adays is a desired need, certainly with modern technology i.e. Can Bus for example, The 3000 has the ability to look at up to 3 data packets at one time whereas the 4000 series scopes can look at upto 12 data packets, giving the user more information to view at any time making diagnostics simpler and quicker.
The 4000 is faster at sampling than the 3000 series scopes and again this is a desired need for new technology such as FlexRay but with common technology aswell.
Another key feature to the 4000 series scope is that it has the ability to look at 'Frequency' through the hardware of the scope i.e. as a coupling > DC > AC > Frequency. This again is a need for modern technology where we are starting to see a significant increase in digital electronics i.e. Digital Air Flow Meters. As engines produce more power and emission laws get tighter there is a desired need to make response times quicker from sensor to ECU. This is where digital electronics are starting to take form. With the 4000 series scope you can diagnose a MAF sensor that has a digital output in the same way you would with an analogue output.
In regards to our high end scopes, there is no need to go outside the Automotive Scopes. The 4000 has been designed to meet all the current needs for the Technician to be able to identify and diagnose virtually any fault within the system. The 4000 scope is also a 12 bit scope which gives the user an extremley high level of detail so signals such as ignition have all the detail to view the characteristics such as Burn Time, Coil Oscillations and Negative Polarity. Some of our top end scopes are designed for different markets and have only 8 bits of resolution and this would kill detail where its essential in Automotive so you really do need to keep to the Automotive Range.
In terms of software, the 3000 series automotive scopes are supported fully in Pico Automotive Software so you can use it in the same way as the 4000. Depending on your budget and you level of use with a scope, I dont see a reason why buying your friends 3000 scope would be a disaster, it would certainly give the ability to be apart of a ever growing community of PicoScope users worlwide but more importantly give you the industry leading oscilloscope.
Long term you may want to look into the 4000 series scope but this depends on the kind of vehicles you work on and what kind of technology you deal with. If your answer like so many others is that you work on everything, old and new, petrol and diesel then id consider the 4000 series scope.
In terms of your accessories, like many other OEM's these should be fine to use with the PicoScope, all you need to ensure is that the input of your current scope is 1 MOhm impedance as this is the case with our Automotive Scopes so this will ensure that they are compatible.
I hope this helps to answer your questions and gives you an idea what you feel you need.
If you have any further questions or queries then please dont hesitate to get in touch.
Lee - Automotive Technical Specialist