Hmm, lots of misinterpretations here...

The "better" design of any plenum boils down to a number of things. First of all, the application, is maximum power the interesting bit or a high average power output? What boosts will it be running? What flow velocitys will it be experiencing? Et.c.

Saw a few MIS-intakes as well as the Mountune one. The MIS is nice stuff for restrictor-based engines running fairly high-boosts throughout the whole register, but not very interesting on a car without ALS and very efficient turbo regarding spool-up. The flow capacity without boost is not an interesting one... But sure, some prefer high outputs and driveability like a Lada for the rest.

Have not been looking on the Mountune piece irl, but judging from the single picture it looks to be pretty much like the MIS in one way, though the inlet into the plenum seems to be more efficient for lower boosts. Basic assumptions here based on shit nothing

Spacing out the original plenum, in standard version, works quite well for a long time when doing a "regular" 400bhp on a cossie, with all that this means concerning boost and so on. The fact is that on so much higher boosts than standard it serves way too much air for the 4th cylinder, and therefore this solution is not very nice for high outputs... In the case you are not fancying playing peek-a-boo with the crank through the top of the pistons

The swedish Mike R plenum? Suppose that is a TG Racing piece. A nice plenum for higher boosts indeed... But as always theres downs and ups.

Wont comment the last one