Well I have only been pouring my own since back around May or so, but before hand I did at least 3 months or more, of reading up on it so I had some clue as to what NOT to do.
In amongst my research I was also concerned with whether to use a GC or not. My main goal was to produce some hunting boolits for my 454 which as you know runs a bit on the high side of pressure in most cases. This said I also have a 41 and 44 magnum as well as a 45 Colt and a couple of .357's thrown in for good measure. I am not cheap, but realized that getting them all to shoot GC boolits was going to add to my expanse.
In doing the research the reoccurring theme was proper alloy, fit, and lube. this said I saw where many were actually turning the GC portion of the mold off and simply going to a straight plain based boolit.
The GC serves two purposes, one it helps to protect the base when used with higher pressure loads, the other is to help seal off the bore where a slightly undersized boolit might be used. This said "undersized" should not be taken as grossly undersized, as in possibly using a boolit designed for a 9mm in say a 38 Spl. as the result would still be considerable leading even with the GC.
If you have slugged your barrel, and have a boolit which is roughly .0015 - .002 larger than the bore it should work fine within the limits of the alloy. If your using straight lead, then your obviously not going to be able to push them as hard as you would if using say Lyman #2 or similar. This said you can also have them too hard and get leading as well. Given a proper sized boolit however, with an alloy of around a 10 - 14 BHN, and a good lube like Carnuba Red or similar, you could/should be able to at least get up into the 1200fps range with standard PB boolits. Much faster than that however will depend on your powder choice and the firearm your shooting them from.
In my personal loads I have run some Oregon Trail PB's up to around 1350fps with no issues, but I haven't a clue what their exact alloy is or the exact hardness. One other thing to consider if you DO start pouring your own, they will grow slightly and get harder with time, similar to concrete. In other words, pour them and then wait at least a week or more for them to stabilize before sizing, and beginning to check for a standardized hardness of your alloy. Usually it is best to pour up your ingots, and check them, and maybe pour up a few from the batch to use as test samples.
With my straight WW alloy, I have only used the PB in a 230gr for my 45 ACP, but I do have a few hundred poured up for each of the above calibers ready to try out, I just haven't been able to manage the time to do it just yet. I concentrated my efforts on the Lee .452 - 300gr RF GC for the 454 to use while hunting this fall, and even though I have three loads which work fine as far as function and accuracy, I am still fiddling with getting them to just where I want them, while at the same time trying to work up a load for my new 45 Colt.
Like mentioned, give the folks at CB's a look, sa well as looking at the writings of Glen Fryxell over here at LASC,
Glen E. Fryxell, Cast bullets and firearm information and history
