subzero can do the short runner ones too ... I believe they simply cut the standard runners and attach the plenum to it.
I would have to say the topic of plenums is rather opinionated. If you don't want to spend a big amount of cash on your car simply leave this area alone and make do with the mods in other areas. RB25 Aftermarkets plenums have very little power increase for those still running the stock turbos as the stock plenum will out flow the standard turbo. The standard plenum from what i have read starts to run out of breath once you get up around the 350rwhp. The general rule of thumb is for every PSI of boost increase your meant to see approx 7-9 hp (providing all other areas of the engine are efficent, obviously differs from turbo to turbo too.). But once you start to make over this hp mark the power increase as to each PSI of boost pressure added decreases.
Runner length also plays a big part in engine response and behavour. The longer the runner (providing the runner has decent flow properties), the slightly less engine response (read:lag). The shorter the runner the quicker the engine responses. The longer runners however increase capacity of the plenum system so to speak which inturns gives the affect of a much larger plenum that what is actually there which means higher HP support.
In my opinion cast plenums are always much stronger than the sheet metal fabricated ones. While some sheet metal ones can give no problems at all they still have the potential to split and fail. I have heard of a story of a sheet metal fabricated plenum blowing apart while on a dyno and doing damage to a vehicle. This is almost a worse case scenario though. Usually if anything do go wrong the plenum would crack around the welds if at all.
Another issue with aftermarket plenums is the positioning of the bell mouths (if any) and even air distrubition. This has the potentional to cause more problems than its worth. Personally when i see a standard rb25 plenum with the throttle body cut and moved to the front of the plenum i shudder. The standard plenum was not designed to have air enter from this point so air distribution inside plenum would not do ideal and could cause one or a number of cylinders to recieve a vastly different amount of air to others, which in turns causes leaning.
I'm not going to say which plenum I think is best as they all have their good and bad points. I have a Greddy plenum on my R33, it was on there when i bought the car so I'm kind of biased, but that doesn't necessary mean its the best plenum.