Have to admit I'm not totally impressed by the Givi brackets, there's a definate weak spot on the back bracket, so I don't put a lot of weight into it usually- i've got a spare pillion seat with some ally tubes bolted on which I use to carry heavier stuff. Topboxes are ace... Especially with go faster stripes
What a difference it makes when touring to never worry about your gear, whether the tailpack has dropped off or leaked... And it's just a wee bit more secure too (though don't kid yourself, it's not going to stop a determined thief, the locks are feeble- but it could put off an opportunist.) You can buy a rack base fairly cheaply, and bolt that to a pillion seat, if you want to save a little but it makes it a pain to get on and off the bike...
Mine is, I think, 42 litres. Bit of an awkward shape, it'll hold a lid but only just and only if it's in just the right spot. I'll probably get myself a Maxia before summer, and maybe a smaller one as well for day to day use, these big 'uns are a pain in traffic. Is the Maxia still the biggest? It's huge, I know that much.