I know this style of wheel bolts makes things even more of a PITA but i wouldn't have thought they'd be harder than the usual grade 10.9 used for wheel bolts? More important than 'colbalt' or other 'fancy' drills is decent quality i.e. Dormer, Presto, Sherwood, Guhring. HSS-Co (there's two flavours, M35 is 5% Co, M42 is 8%) are harder than plain ol' HSS, the upside is that they can be run at slightly higher speeds without softening, the downside is that they're more brittle i.e. easier to snap. Having said that cheap colbalt drills are often junk compared to quality HSS... too brittle, often poorly ground so they don't cut properly etc.
HSS-Co can be handy when using a hand drill as they don't have the range of speeds- rpm is related to diameter as cutting speeds are figured in metres/min or surface feet/min. Larger drill and/or harder material = slower speeds, too fast and the tool rubs instead of cutting, overheats and softens. The other problem with having to using a hand drill is feed. Hard materials/larger drills need leaning on to get them to cut rather than rub, easy enough when drilling something in a drill press or lathe, trickier when working freehand and trying to keep the hole straight. A DIY variable speed drill (rather than something with a gearbox) doesn't help either as you lose all the torque when you slow the rpm and then it stalls/overheats when you lean on it. Some cutting compound/coolant, while a ball ache with a hand drill, will help some too
FWIW with HSS tooling mild steel is typically machined at around 90ft/min give or take. Tool steels and some alloy steels as low as 30 - 35ft/min. For a 10mm drill bit that equates to around 900rpm for mild steel and 300-350 for the tougher flavours. 13-14mm drill and it's more like 600 and 200rpm respectively. Colbalt can be run around 10% faster or, at the same speed, will hold it's edge for longer
It is possible to attack this sort of job with a welder but it ain't easy and a MIG won't cut the mustard. Using a bit of thin wall tube down the bolt hole to protect the wheel you build up a pad of weld on the remains of the bolt until you're past flush and can weld a nut on. Again, not easy as you're working blind for most of the job.