you can't use a hole saw with a pliot bit for drilling glass you need a diamond core bit my bit's are coming in from hong kong in the next couple of weeks and i might post a forum on it.
Theire are a few differeny way's to do it your links will specify a couple if you could use a wood hole saw i sure would because i already have a couple but you can get the bit's for cheap in hong kong and i hear they work.I can try to find the sight again.
One thing I also do when drilling a tank is to make a support which goes inbetween the glass, I'll cut a 2 X 4 to length. This helps prevent the glass from chipping as you go thru. Chipping occurs when appling a little to much pressure as the bit is at the end of its job.
I have drilled holes in flat plate glass useing a diamond core bit. I have never seen one with a pilot bit or heard of anyone using a pilot bit. If you wish to try it I would recommend doing it on a piece of scrap glass first before trying it on your aquarium. Personally, I think the chattering it would cause will break the glass but hey, I could be wrong.
I would think that if you are using a drill press then the pilot bit is not necessary, but probably wouldn't hurt. Where the use of the pilot bit would be helpful is if you were using a hand drill. It would prevent the drill from moving around on the glass. I would still reccommend using a drill press so that you get a perfectly straight hole. If you use a hand drill and don't get it straight, the cant of the bit could bind against the glass and you will end up with a broken tank. Just my $.02
OK I made a practice cut on a 1/4" glass with the pilot bit and it worked perfectly! I just set the clutch to a low setting as to not bind and break the glass. The pilot bit made it much easier to start the hole[I didn't use a jig] and the bit didn't ride or slide across the glass. I now plan to use the pilot bit to start the hole and remove it after the bit goes through the other side, when the bit is almost through i am going to put the pilot bit back in again and drill from the opposite side so I don't get any chipping of glass around the hole when the bit comes through. Any thoughts or ideas would be greatly appreciated along with any criticism that may change my mind or make me do something different.
Please respond with any and all input!