To me, the only "real" reason to get a mac pro is because of the hard drive options which are really limitless.
They are limitless because can leverage external drives if necessary ( very high speed SAN (FiberChannel, aggregated 1GbE, 10GbE, etc.) or SAS/eSATA connectors direct attach storage connections ) . The current iMacs largely leveled the playing field on that functionality. There are some gaps on cost effectiveness and breadth of coverage, but it isn't that hard to attach 10-20TB to an iMac anymore and get multiple 100MB/s out of it.
If restricted to just internal drives it is quite limited because there are limited number of bays to put drives in.
If you need over 32gb of RAM or 12 cores you know who you are and what you are doing. For most other people, an iMac is great EXCEPT for the hard drive limitations.
What the Mac Pro is sorely missing is 4-6 cores and marginally higher than iMac GHz throughput. There are a sizable set of folks who have mixed workload. Some subset choked on legacy software (or somehow necessarily scalar, but that's a smaller subset ) and other software that can scale past 2 and at least to 4-5 cores comfortably.
The dual pacakge set up isn't quite as old as the 4 core offering which pretty ancient at this point ( on the verge of being
two Intel tick/tock cycles behind.... ). Without a healthy single package offering the whole Mac Pro line-up is in jeopardy. Both are likely needed for a viable offering.
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My only concern is that the mac pro is 2 old, but i cant wait anymore i gotta get one of the two, what do you guys think?
I think that budgets make a big difference in deciding between the two. Depending upon the system you need for your workload the overall system costs won't be the same. For example, highly storage skewed the Mac Pro may work better. If lightweight local storage then the iMac has traction.
It far more depends upon what the workload mix is going to be rather than the hardware. Especially if primarily just dealing in the intersection in the border area between the BTO iMac and the entry level Mac Pro. That's where the product overlap is highly muddled these days.