I'm running Mk X engines atm, which state:

+15.8 Flight Speed
+20.4 Turn Rate
100% recharge time reduction to Slipstream Drive
Full Impulse: 101 Flight Speed

Now, I was just about to get the Mk XI, when I noticed:

+15.8 Flight Speed
+20.4 Turn Rate
100% recharge time reduction to Slipstream Drive
Full Impulse: 101 Flight Speed



What's all that about then?

littrially these days the only reason to get a higher mk engine is for the set bonusus of higher mk sets.

The displays don't seem to be accurate.

I was comparing a Very Rare Mk VII and a Rare Mk XI Combat engine, and the Mk VII appeared to be superior in what it displayed, regardless of where I was. When I actually swapped the engines (flying around Sol system) there was a huge difference in actual speed.

I could be wrong, but I think you have to un equip the engine from your ship and compare them in your inventory to get more accurate stats.

I think some of the stats are bugged. When I look at my shields on my ship in a mission, it states I only have around 8500 hp per facing, but when I check under Defense on my ship tab it shows each facing around 15,100 hp.

Also been noticing some little bugs here and there. When you search the exchange for Vice Admiral level items it will just bring up a few, however if you put in Mk XII in the search box it brings up the max 400 items, but they don't show up if you just leave the search field blank and select vice admiral and any quality. Also some item stats don't seem to display right.

Always wait until you're in Space (not Sector Space, regular Space) to test weapon stats. You won't get an honest bit of info on them until then.

OP was on about the Omega Engines. The stats are the same for each kind of mark.

I tried that as well, there wasn't a difference. It wasn't a rare vs very rare either, I remember now that both were Combat [Turn] [Speed], but I had been using a Mk VII and just spent cash on a Mk XI. My thoughts were "Why are these the same? Did I just waste money?"
That's kind of what I was talking about, the two engines in my inventory had exactly the same stats (same mods, different Mk), so I went into Sol and they still looked the same. When I actually put them into my ship and flew around, the Mk XI version was faster and turned better.

(They weren't the Omega Engines though, so there may not actually be a difference in Mk for those.)

Fairly common problem, I find. I've gone through 3 different levels of those Efficient Impulse Engines; the info for all 3 was identical, but their actual performance was different.