I was not talking about the temperature inside the ISK. I am referring to the temperature of the air surrounding the ISK ("PC's ambient temperature" as referred to by Steve some posts above).
Yes there are some misunderstandings: in your first post I thought you were talking about the cabinet (furniture, as in italian "cabinet" can be referred to a case/enclosure), and my answer was related to that, while in your second post, as you were talking about fans, I intended you were referring to the ISK enclosure, and thinking my first answer was somehow wrongly directed, my second one was related to the case itself.
Anyway, both the temperature are (you know) related.
As you don't have active cooling into that cabinet, you rely upon convection solely.
So, summarizing, hot air rise from bottom to top: but at the top there's another shelf, so you will likely experience some heat build up.
With reference to that heating, although fluid dynamics is a complex matter, currently I don't think the side fans may help substantially pushing the hot air away from the relevant shelf, as the volume outside the case is much larger than the internal one and a fan isn't a nozzle, so it cannot direct the turbulent flow straight out from the impeller.
The ISK airflow design is fairly simple: it has a small inlet on the bottom and exhaust from the top.
When you flip it on the wide side, the inlet is higher than the outlet: it can still works, probably less efficiently as you loose the chimney effect, but in your specific scenario that inlet will stay right there where the heat build up occurs.
So that (now I'm reprising my first answer) you may likely have such a scenario, under load: the fans exhaust the hot air from the right side, most of that air will be entrapped under the top shelf, and that's where the inlet will breath, and no fresh air will go inside the case, iterating this process. Given that, I think that a modest 5°C rise may be a bit optimistic, particularly under load
(around the case, between the shelves).
If the case had not a shelf over it, things should go surely better.
Two further considerations: SPCR tested the 65W ISK 300 with a cool Core 2 Duo E7200, and you can see it ran pretty hot
; up to now I think that with a powerful Haswell Core i5/i7 you may only have worse temps (but that's just my not-so-educated guess).
As a consequence, it shouldn't run quietly: probably it won't be unbearable, but more probably that not it will be far from quiet.
Last but not least, the proprietary fanned PSU of the ISK-310 is fairly loud, so IMO you have to swap it.