I'm trying to order a set of spark plugs but i'm getting 2 separate model numbers:
PZFR5F-11

PZFR6E-11

Which is the correct one?

 

This has been covered in lots of previous posts. The type-s uses a "6" and the non type-s uses a "5". Different heat range. What's your car?

Then for NGK, there are platinum / OE style platinum / iridium / oe style iridium all at different price points. If you get the heat range and the gap correct, they will all work pretty well.

(Data point : I use the ZFR6FIX-11 for my '01 CLS. 2 sets, 100,000 miles since.)

 

I put IZFR6K-11 in my car a few weeks ago. The plugs that were already in the car were PZFR6E-11

P = Platinum
I = Iridium

 

I put NGK Iridium IX's a few months back.

 

How good is this NGK Iridium IX's compared to the NGK laser Iridium.

 

The Iridium IX is a non-OE plug. The Laser Iridium I believe is the OE plug from 2003 and above. (Before that, OE was Laser Plat).

I have used the Iridium IX's only because they are the most readily available in stores (and cheaper at about $6-7 a piece). The laser iridium / laser plat tend to cost more and have to special order or mail order.

They all last 40-60k miles no problem under normal conditions. I doubt you will be able to tell "how good" a plug is beyond this.

 

My car is an 03 and had laser platinums in them. IMO it's probably just a 6MT thing.

I put laser iridiums in mine because I guess I'm paranoid and wouldn't trust a $6.70 spark plug to last 7 years or 105k miles.