Longer core means more chance to shed heat but also means more pressure drop.... so you neeed to run more boost at the turbo to get the same boost at the plenum, which means more heat......can be self defeating but comes down to eff of core
Same deal with cross flow v vertical core. The beauty of the vertical core is the huge increase in cross-sectional flow area and therefore much less pressure drop. Comes down to whether the core eff is good enough to shed enough heat along the shorter core path....internal turbulator design becomes very important and you are looking at the high end $$$ cores.
I have run both and not much to pick between them for a street car. I would say it's a difference only a race team would be chasing. For a street car, it mostly comes down to packaging.
What you have to keep in mind is that for a street car the IC is mostly working as a heat sink so the MOST important aspect, after flow, isn't the eff of the core, it's the MASS of the IC...big heavy suckers are better. Why? because you aren't in a steady state heat exchange...all the initial heat exchange is from the core and end tanks heating up thus pulling heat out of the intake charge. The more initial heat sink capacity you have the better. The on/off nature of street boosting means the core can soak the heat and then shed once you are off boost.
On the track where you are always on boost you need good steady state heat exchange where the core can shed heat to atm efficiently continously.
This is why bar and plate is generally best for street and tube and fin is best for track work (tube and fin also much lighter with weight being a major consideration for a track car).
As with most things it's a trade off and you need to find the balance. For mine the best compromise for a street car that sees some track work is as large a bar and plate FMIC as you can fit. For me that was a 600x300x100mm core.
Hope that helps explain the pros and cons a bit