Whats the most I can do to this Mac Pro

If I were you, I'd keep your eyes opened for at least a 2009 (4,1) model which you can upgrade to 5,1.

I was lucky enough to get an 8-core with 256GB ssd and 24" Led Cinema Display for a really good price. You can also get the 4-core version, which can be later upgraded to quite powerful 6-core Westmere

If I bought a 3,1, I'd probably consider it as a bad investment. I'm really happy with my 4,1 (5,1). Go for it too! =)

I have been contemplating the same course of action but have decided to wait for the next upgrade of the new Mac pro because:
Old Mac Pros are old technology and hardware and on the way out.
Upgrades are difficult regarding high speed wifi, thunderbolt, etc and I can't be bothered to put up with the hassles of someone else's cast offs.
All other macs seem to be intent on grilling their innards with only moderate graphics loading and I see the new form Mac Pro as Apple's only real world, work station computer.
I will never buy another all-in-one just to see a good screen lie idle because the rest of it is cooked.
I deplore Apples fixation of thinness just for bragging rights letting professional engineering concerns go to pot.
This will be my last computer and if it doesn't work out I am taking up tiddly winks.

Hello,

If you can get a pre-2009 MP on the very cheap, then go for it and resell it later. Otherwise, stick with 2009+ MPs. Just about everything is upgradeable in them, and they still blow just about every iMac out of the water (except on raw CPU speed, where quad iMac can have an edge on quad MPs).

The trick is to get them at a good price and decide, in advance, which upgrade you want/need to do. Many people here plan on keeping their 2009+ MPs for a long while yet. As I said, the only weak point is the CPU speed. Everything else can be upgraded to better than current Mac Pro performance.

Loa

any MacPro 4,1 + is still good investment.

Honestly, currently technology is so fast that you won't feel that much difference anymore.

I just gotten MacPro 5,1 with quad 2.8 which was still good, but just upgraded CPU to 6 core 3.4 Westmere X5690 and BT to 4.0 and 801.11ac using 94360CD card as well as installing SSD to create fusion drive and I believe I am up to par with other pretty solid system.

I was running hackintosh with i5-3570K which I felt pretty fast but my so called old MacPro that I just upgraded blows it away.

The listing you are looking at is 3,1 which doesn't get much support. I wouldn't get that.

don't get it, you cannot return it.

Having just bought one I'd stick to the 2009+. I waited for a while but eventually got an as-new 2009 Quad for $500. It was in great nick. I put a few bits in it, namely a 3.33 6 core, an Apple 1TB SSD blade (Sintech adapter), 16GB, flashed ATI 7970, BT 4.0 and AC WiFi card and it flies. Quite a cheap box to build. I had an i7 Quad Mac Mini before it was struggling a bit at times.

Another vote for a 4,1 or later. I have a near-baseline 4,1 that has done fairly heavy software development duty for over 5 years now, and it's still nearly as fast as the fastest of the corporate VM's that the other dev guys use. I'm about to embark on RAM and CPU upgrades and I expect to get another 2 years minimum out of it, probably more like 4, for a fairly minor $ investment. If I feel like it I can add SSD as well for another speed increment. The machine is extremely quiet and in 5 years I've had one failure. (a hard drive died, easily replaced.)

The 3,1 isn't a bad machine, from what I hear, but the real upgrade capability starts with the 4,1 IMHO.

A better question is what are you planning to do with this MP? You should state what apps you will use on it. There has been written too many times that the 3,1 is too long in the tooth to be worth while. It depends on the price and intended use. A great percentage of people post their specs but not what apps they actually run. Not only do they not post what apps they run, they never compare the 3,1 to other computers. It's never stated or comparison videos placed on Youtube to show the "short comings" of the 3,1. No one states you can do "this, this and this" on the 4,1-5,1 but not on the 3,1. And I don't mean upgrades so more "specs" can be listed. There seems to be more of a "spec" comparison than an actual MP shoot out!
The thing to watch with that 3,1 is that the video card was not listed and it only has 6gb of ram. Ram for the 3,1's is expensive!

Seems plausible enough to me...