version 3.5? and what computer?

I have an old solid but still good MacPro but it runs max to 10.7.5 - Aperture there is limited to 3.4+ = On my MacBookPro I do have Mavericks installed and also have 3.5.1 Aperture - but that means that if I [as I just did] return from a trip where I used Aperture on the MBP I can't move it for use to my MP - which is my main machine.

I can't afford the new MacPro and would be just fine with the old model, and buying refurb or whatever = but what model is new enough without being too new?

I like having the 4 drives internal by the way, which is why sticking with the MP model is fine for me = I do NOT want to use my iMac or external drive bay. I just want to update the MP I have now or get a newer model of the same type of thing.

Suggesitons???