First opening pair of quicks in test cricket weren't they? I remember reading somewhere that they caused a fair bit of upset over here due to their bowling being rather more intimidating than what had gone before. Perhaps an inspiration for Jardine 10 years later?
I've read in a few places that they were the first pair of quicks but when I started to check that seems to be an oversimplification
Pre-war it was usual to open with a fast man and a slow or medium pacer. I looked at Tibby Cotter, who by all accounts was very sharp, and in 1911/12 and 1912 he tended to open with Bill Whitty who is described as fast medium, and his predecessor as the Aussie tearaway, Ernie Jones, the bloke who legend has it bowled one through WG's beard, sometimes opened with Bert Hopkins who was described as fast medium as well
As for England a lot turns on what you classify Syd Barnes as but Frank Foster and Johnny Douglas or Barnes opened up in Australia in 1911/12, although none were express pace - interestingly Tom Richardson would generally open with Bobby Peel, who was orthodox slow left arm, and did so throughout the 1894/95 series despite Bill Lockwood (genuinely quick by all accounts) and William Brockwell (fast medium) also being in the side.
That said on debut in the final Test in 1893 Richardson opened the bowling with Arthur Mold, also said to be genuinely fast but that was clearly not an experiment England wanted to persist with - I'm not so sad as to have thoroughly checked but I think that was the first instance of two all out quicks opening the bowling in a Test
I think a large part of the problem with Gregory and McDonald was the age old one of England having no one fast themselves and therefore being unable to retaliate.