Would one with permeability of 50 (instead of 2200 for N87) be "gapped"?
Yes... sort of. But ferrites aren't common in that range -- you'd be looking at #61 or #67 NiZn ferrites, which are expensive, have low Bmax and very low hysteresis/eddy current losses: they're intended for very high frequencies.
The fundamental problem is, energy density goes as 1/mu. So hi-mu cores are great for transformers, which ideally store no energy, and terrible for inductors, which must (note the distinction between transformers and coupled inductors, which also have multiple windings).
Air having the lowest mu, also has the highest energy density; but it's hard to couple directly into air when we are limited to the use of copper wire, so it is most efficient (by size, weight, cost and efficiency) to use a permeable core with an average mu of 10-100. (Average meaning, if the core is gapped, you can find the effective permeability assuming the length is the same: mu_eff = l_e / (l_e / mu_r + l_g), so that a core with l_e = 100mm and mu_r = 2000 with l_g = 0.5mm air gap (the gap being mu_r = 1), has mu_eff = 181.)
And yes, at first i tried a regular N87 ring of the same size and 10 turns. 1000uH of inductance, but it saturated pretty much at once. 
In fact, it will saturate in:
t = Bmax*N*A_e / V
so if, starting from zero current, you apply a square wave pulse of 10V, and it has Ae = 100mm^2 and 10 turns, a ferrite with Bmax = 0.3-0.4T will saturate in 30-40us. (Note that 100 mm^2 = 100u (m^2), so SI units work out very handily when using both us and mm prefixes.)
In that time, the current won't rise very far. If your application requires pushing a current through that poor inductor (like a current mode buck converter), you'll have some problems...
I'm still trying to wrap my head around how to pick the right magnetic material and it's size.
Permeability is the only parameter specified, and yet 3 turns on 2200 material is not the same as 40 turns on 50 material of the same size, even if the inductance is the same.
Just doing the math gives me permeability of no more than 70 for the given ring size, if i want 6A, and thus 41 turn on a material of 50.
But what does the math mean still eludes me.
If nothing else, the Maxwell stress Pm (literally, the pressure due to a magnetic field -- the attraction or pressure you feel between two magnets) is also the energy density (because Pa == N / m^2 == J / m^3!), and since Pm = B^2 / (2 * mu_r * mu_0), you want as low an [average] permeability as practical.
Another way to put it: if you're eyeing a particular ferrite core (E-E or whatever, say), you know you need at least this amount of air gap (setting mu_r = 1 and finding v_g = E/Pm, and then l_g = v_g / A_e) to store the energy you want to put into the inductor. Of course, the energy is given by E = 0.5 * L * I^2. You would finally set number of turns based on inductivity (A_L) for that core, at that gap, and the desired inductance.
Or, you can do it by flux, because inductance is the conversion factor between flux (the volts-for-how-long you applied to the winding) and current (how much the current changed during that time). If you need 2A at 10uH, that's 20uWb == 20uVs. This exactly fixes how many turns are required for a given core, regardless of gap: Bmax, V and (t or 1/F) are connected, absolutely independent of gap or mu. Finally, once you know the core and number of turns, you set the gap based on the inductance required.
For cores of fixed permeability, you don't have the added degree of freedom (adjustable gap), so you really just run through a parts listing and find one with enough volume to store the energy, that's also big enough to put on the turns required for your inductance. Material choice is based on frequency and losses (#26 or #52 powdered iron is... just about useless for anything really.. #8 and #35 are pretty good for most purposes, #2 for high frequency and Q.. and other materials like MPP, Kool-Mu, etc. that have varying properties).
Makes me wonder how big a grain of truth is behind audiophoolery's claims for their 5-digit-price coupling transformers and filters.
The transformers are usually made with high-mu materials like 50/50 NiFe, permalloy or supermalloy, which are of course fairly expensive, in and of themselves. That would almost justify the $20 price tag. Special winding arrangements (interleaving, bank winding) to reduce leakage inductance and stray capacitance might even justify a $40 price tag.
Beyond that, it's allllllllll marketing.
As many buzzwords as you can throw at it: silver wires, gold wires, sonic clarity, soundstage, presence, etc.
And for filters, you can make reasonable low distortion coils from gapped iron, gapped ferrite, or just go naked (air core), which will similarly increase the price in a relatively marginal way, but anything beyond that... you know the Dave Jones buzzword.
Tim
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