We cannot know about Gimeno/Emerson for the period 1960 to 1967.
Sure, Gimeno improved after turning pro, but so did Emerson improve during these years.
Emerson was great on clay, winning at Roland Garros in 1963 (after outlasting Kunhke and Pietrangeli in 5-set marathons) and 1967 (defeating Roche, the defending champion, in the final).
Gimeno did, what?, at the 1960 Roland Garros, where he played twice that year, amateur and pro?
Seeded third in the amateur Roland Garros, he lost in the quarters to Pietrangeli.
Lost in the pro version of Roland Garros to Sedgman in the quarters, and to Cooper in the fifth place playoff.
In 1961, lost at Roland Garros to Trabert in the quarters, to Trabert in the Kramer Cup semi at Barcelona (6-3, 6-4, 6-1), and to Cooper at Vienna, your home town.
Yes, all on red clay.
In 1962, Gimeno did better at Roland Garros, beating Anderson and Olmedo, before losing to Rosewall in the final.
In the 1962 Kramer Cup semi at Turin on red clay, Gimeno lost both of his singles to Hoad and Rosewall in four set matches (losing to an over-the-hill Hoad 2-6, 6-1, 6-4, 6-4).
At Roland Garros Pro in 1968, Gimeno lost in round of 16 to Fred Stolle.
I would expect that these clay results would have been surpassed by Emerson had he been in the pro ranks, Emerson winning over tough clay fields at Roland Garros in 1963 and 1967.
Really, no contest.