At least the XB500 leaks less than XB700 as the vents are so much bigger on XB700 but it may still be enough of a prob if wearing in public in quiet environments, in noisy environments or even at schools during breaks for example I'm pretty sure it wouldn't be a prob.
As for the Sennheiser HD 212 Pro, I'm using these at my parent's place whenever I go for a visit there and I'm there atm and listening to them atm, I used to use these before as well before on my own comp. What I like about these that also would fit you would be the fact they shut off ambient noise very well and they are very lightweight and doesn't leak any sound at all. The bass by my personal boomy / punchy bass rating I'd rate it 55/45 compared to 45/55 for the XB500. So the 212 are slightly on the boomy side but they also pack a lot of punch. The bass quality sounds a bit worse than on the XB500 as well but it's not horrible by any means, in fact it's the strongest point of the headphone really. As for the quantity, well 212 has slightly less quantity compared to XB500 but it's got more than XB700 so somewhere in-between those. The overall sound signature is somewhere in-between aggressive and laid-back and the XB500 is more on the aggressive side. The midrange is quite recessed and the highs are very bright and "thin" and lacks the fine detail heard in better headphones, XB500 is the opposite with smooth highs but better quality even if they don't stick out as much cuz on the 212 they do it in a rather bad way that can be ear-piercing sometimes depending on your EQ settings as usual. With precise EQing you can get relatively good results though for both for the price, both headphones really benefit from EQing a lot and XB500 needs it especially to "unsmooth" the overall sound for better clarity that is got by having especially 250 - 500Hz range lower and raising 4 - 16kHz range. 212 Pro needs a boost especially at midrange, ie 1 - 2kHz and also especially 250 - 500Hz so a bit of the opposite compared to XB500 or else they sound rather boring and "lifeless". The 212 are also easily driven, not quite like XB500 but fairly close so an amp isn't a necessity at all (more like an amp won't improve the sound by any remarkable amount). Oh and another interesting point I'd like to point out is that they are suprisingly well fit as gaming headphones if you disregarding sound quality, it's easy to pick out the directions the sound comes from on these headphones.
Have you concidered an AKG K 518 DJ though? They are good for portable use, they look awesome (IMO at least), very compact and lightweight and these packs a lot of bass punch & impact but they are rather tame in the sub-bass range below 80Hz or so. They are like the opposite of XB700 in bass, if I'd rate the XB700 like 70/30 % (boomy / punchy) ratio then the AKGs get the opposite 30/70. The bass punch is very close to that of XB500 but they don't do dubstep or hardstyle music with deep bass justice IMO due to the poor sub-bass extension. Another thing you need to know about them is the comfortability, non-stretched these sit very very tight on your head, the clamping force is so huge I got earpain after 20~30 mins of use but after stretching them overnight for 3 nights over the box they arrived in, that problem disappeared. They are also very easily driven, nearly as easy as the XB500 and I've found that they sound rather good from a lot of different sources, especially straight out of my TV so that's where I mainly use those these days whenever I don't want any1 else hear when I'm watching some silly programs like Idol.
They share a bit similar sound signature as the XB500 too with very smooth/dark sounding highs a reasonable midrange that has the vocals sticking out clearly. The soundstage is however fairly enclosed sounding, XB500 has a more open or airy sound. The price is pretty much the same as for the XB500 too.
Hope this helps.
