Analogue-sequencer

> I never update my P3.
> Can I put the v4 sysex file in cubase make the right 
> connection and go?

First thing I would say is that if you have not successfully backed up the
contents of your P3 memory via sysex, you should learn how to do that first,
so you can reload your work-in-progress if you revert to v3.

I'm not Cubase user, so I don't know if it has suitable sysex library
facilities.
Without using handshaking to control the flow of sysex, you need to be able
to have an arbitrary delay between the end of each block, and the start of
the next, to ensure that P3 has time to process incoming data.
The sysex window in MIDI-Ox (excellent shareware utility) is ideal for this.

If you have a PC, the P3 Tools software is by far the best way to manage
dumps of P3 v3, and also has a great firmware update utility that will work
equally well with the v3 or v4 fimrware images.

If Cubase can play back a MIDI file including sysex, the .mid version of the
firmware includes the necessary delays to install without handshaking.
Windows Media Player can be used to play back the .mid file too - you just
need to ensure that the default MIDI playback device is the MIDI port you
have connected to P3.

If you have a Mac, I can't offer much help, other than to jokingly ask why
you didn't buy a PC ;-)

> O and I have serial #1077.
> 
> Do I get problems with the bootloader?

That should be fine.
If the current version of the firmware is 3.1.002 or later (version is shown
on the display during boot), then no bootloader update is required.

Best regards,
Colin Fraser
Sequentix Music Systems Ltd
http://www.sequentix.com