hay iv been using a macpro 3.1 2.8ghz dual cpu 8c for the last 3 years, been editing video 1080p,using photoshop making websites & playing games + general stuff (had 1SSD,3HD’s & gtx660) been rock solid since i had it
if you buy one check how much ram it has, ram for them is not cheep
i use the slower 667hz stuff which is a lot cheeper. mine came with only 2Gb had to upgrade it to 18GB which seems fine for most stuff i do (1080p video editing, photoshop etc..) also check to see if it has wifi & bluetooth and check the cable is ok.
i recently picked up a macpro 5.1 (same as a 4.1) single cpu 2.8gh 4c.
the single core speed is faster (notably so) but the multi cpu speed is slower (not by a lot).
now that only matters if you have a app that can use 8cores any app that can only use 1-4cores will be much faster on the 4.1/5.1.
i swapped out the cpu on the 5.1 to a 6core 3.33GHZ cpu, each core 2/3’s faster and the total speed is about 50% faster (and thats with 2 less cpu cores). the cpu buss & ram is faster too + the ram is a lot cheeper.
for the 4.1/5.1 you can get a 3.46ghz 4c cpu super cheep and the 3.2Ghz 6c is also vary cheep to (both of those cpu's are a lot faster than the 3.1 2.8ghz 8c) you can also get a 3.33ghz 6c and 3.46ghz 6c but they cost more.
so normal use example is on youtube i was not able to watch 1080p 60fps videos without them being relay jumpy on the 3.1 (lots of frames dropped) on the 5.1 i can now watch 1080p 60fps videos without problems (a few droped frames but nothing i notice).
I do miss the sound of my 3.1 tho the fans had a nicer baser sound to them
PS the dual cpu 4.1 are a tad harder to upgrade but nothing bad)
edit the 4.1/5.1 is better than the 3.1 but the 3.1 dual cpu is not to bad
kind of depends what you want to do etc.. a new macmin or imac will be faster for most ppl