Hmm. Re reading my post above it's not very helpful!
Let me share some drilling experiences, which might be more useful!
A good few years ago, I had to regularly drill some small holes through steel castings about 1/2 inch thick! If anybody has ever tried to drill castings you'll know it's tough on drills as you get all sorts of hard spots, not to mention a 'skin' either side!
Anyway, I was given a load of new cheapo drills (Chinese or Taiwanese I suspect) which was a bad mistake! I could only manage 3 or 4 holes max before the drill broke, and that's using a decent drilling machine, at the correct speed, with everything jigged, and being uber careful!
I sourced some Eastern European drills locally (Polish if I recall) and these were better, managing 12 or so holes before breaking, and usable if I stopped after 10, but it wasn't an enjoyable process. The things felt crunchy all the time, as if they were on the verge of breaking!
I ended up using the one old Dormer drill I had in the correct size, and it was superb, cutting the remainder of the 200 holes without any issues! Felt good and was still usable afterwards!
So, decent drill bits are the way forward!
Dormer were good, maybe even the best, and I treasure the old ones I own, but they are no good now. The last one I tried was not even Eastern European 12 hole quality, and when I complained they suggested I needed one made from a higher grade of unobtainium, which I clearly didn't, given how the old ones performed!
So, what do I use now!
For metal drilling I have various other British makes such as Cintride and Presto, and all seem to be fine! I have also bought drills through MSC who used to offer U.S. made Cleveland drills which seemed to be as good!
I currently buy from a specialist supplier (Drill Services, Horley U.K. for the Brits here) and anything they supply me seems to be great. There is a lot of Guhring there, but also Spanish made, Japanese, and even South African if memory serves. No complaints!
For most jobs I use regular HSS bits. I wouldn't consider 10.9 particularly high tensile so I'd use them for that too, but just as important as the steel is the setup! Generally, when I'm drilling I'm using a bench drill or jig borer and everything is nicely controlled! Working on studs and suchlike, probably with a handheld tool is a much bigger ask and a much bigger risk of heating the drill, so I'd consider a Cobalt drill!
Use Cobalt anytime there's a risk of getting the thing too hot! Most if the makers listed above offer Cobalt as an option! Most also offer TiN coated too. These have a longer life and are fine for smaller drills you can't be bothered to sharpen, but I don't bother otherwise - and a TiN coated crappy drill bit is no better than any other crappy drill bit!
Finally, make life really easy by adding a squirt of cutting fluid! MSC, or any drill supplier, will have some. The drill cuts better and has a longer life with it!
