I don't mind Kilos for stacking. Not to big, not to small. They are about the size of a 10 OZ bar only thicker.
My other concern with bigger bars is that it's harder to verify them. With a large silver bar, there's a lot more room to work with if you want to fill it with something other than silver. I'd be even more reluctant to go after large gold bars -- there, the only thing they're likely to be filled with is tungsten, but when you're dealing with tens or hundreds of ounces in a single lump, there's a huge incentive to cheat.
And then melting it into another bar before the deal is done. I gamble a little but certainly not $300,000 Worth.
Gold's density: 19.32 Tungsten's density: 19.25 to 19.3 (sources vary) If you're up against people whose technique is enough better than mine to distinguish those, trim the tungsten core with platinum (density 21.45) until the match is perfect. Platinum costs a third as much as gold; you're still coming out way ahead.
I don't pretend to be any sort of big-league bullion trader, but I've seen plenty of articles indicating that tungsten cores are a very real problem. At one point, you could buy tungsten-core fake AGEs from AliExpress for about a quarter of gold spot. I expect you still can. AGEs are just as difficult to fake convincingly as other US coins; if you've got an eye for detail and your guard is up, you probably stand a good chance of catching them. Generic poured gold bars, though? Welcome back to the wild, wild West, or perhaps I should say East...
Easiest way to counter that is to only buy from reputable dealers, I guess. I've been buying from Apmex, so I don't worry about any of that.
Congrats on your milestone. I agree with the 10 oz size, they feel great in the hand. I also like the 5 oz bars too.
Do you collect just bullion as close to the silver spot price, or will you buy other items like coins, commemoratives, etc.
I'm split half-and-half right now with the 10 oz Royal Canadian bars and 90% silver (almost entirely Washington quarters). I will probably avoid any art bars or rounds... most of them don't appeal to me.