I have a bit more time to explain my first brief answers above.
Firstly have a look at this thread for cars with over 160,000km.
100,000 + miles club - Mazdaspeed Forums
We have had three Mazda (non turbo) cars in the family with over 200,000km and no major issues. However my second hand 626 V6 did have some issues and obviously had a rough life before I got it.
The turbo Mazda's are a more highly stressed motor and if they are not serviced regularly and driven properly they can fail prematurely.
My CX7 has so far done 130,000kms with no major mechanical issues and I am hoping to get it to 200,000km. It does have a replacement low km turbo from an MPS3 which will help.
Once you start getting over 100,000km there are a number of failures that become more likely. VVT actuator, turbo seals, timing chain, engine and transmission mounts, A/C compressor, transfer case for MPS6 and CX7 etc.
Considering a dealer will charge you about $2000 to change out the timing gear and VVT it makes sense to me to spend that extra money on a lower km model (usually later year build too) with a full service history and a knowledgable owner.
The DISI turbo motor needs to be driven hard sometimes and needs regular oil changes to remain reliable. There have been a number of failures at high load and low revs, known colloquially as ZZB for Zoom Zoom Boom. Here is one explanation of this.
One of the reasons behind breaking rods and ringlands - Mazdaspeed Forums
I hope this helps.