It is uncommon to find angular contact versions of radial cartridge bearings that are drop in replacements for things like hubs. I'm not positive, but for your Mavic's it is unlikely.. I know that Enduro offers angular contact versions of many of the 6xxx series bearings, but they are often slightly different in width and require hubs that are adjustable for preload without the use of spacers.. so even if they fit, it is possible your version of wheels might not be compatible.. need more information to really say for sure.
As for seals and grease, this is really up to you.. it is very common practice in the cycling industry to grind the races in a way that a 'rubber seal' is non contact and really just serving as a dust shield, so no need to remove the 'seals' in this case. As with so many 'standards' in the bike industry, something like '2RS' in a bearing part number might mean something different from many bicycle industry companies than it might from an industrial supply house.

Years ago at Zipp we started having our Swiss bearing manufacturer grind an additional tiny groove into the bearing race to allow the seal to look like it was contacting, but actually not touch, quite a few companies do this today. We were also the first to use polyamide bearing cages instead of metal and also specified a lube from Kluber that had very high pressure/load rating, but was also rated NLGI 0 which meant that it could flow when the bearing was running to continually replenish the bearing surfaces but also felt like there was hardly any resistance on the bearing in your fingers, unfortunately this stuff was also about $200 per kg, but it was a perfect blend of feeling fast in your fingers and also being fast in the field.

I have seen many teams/athletes and companies using things like open shielding, oils, etc in bearings and can honestly say that it just doesn't work that well under running loads, or adds risk when used in the real world. For about 6 months, Bjarne Riis had this 'bearing guru' work with CSC, he would flush the bearings, put in oil, knife out the rubber lips on the seals, etc.. all claiming these big savings, but the mechanics would get the wheels/bb's after a single day of racing and it all felt like crap and had to be reworked.. we finally sent one of these 'snake oil wheels to the lab alongside a brand new Zipp wheel, the lab found that the snake oil wheel had higher running friction under load as the thin oil was just flung out resulting in ceramic to metal contact. This is why you see experts in this like the CeramicSpeed folks using oil in their pulley wheels (low load) and very high end grease in their hub and BB bearings.

Having said all that.. moving from stock bearings to the fastest bearings available in a wheelsest is worth on the order of 0.8-1.2 watts at 30mph which is certainly a marginal gain, but is also on the order of magnitude of the aero penalty of properly vs improperly adjusted helmet straps or being 2-3psi over pressure on pavement of moderate roughness.