There isn't particularly an operational need for the 6pdr in early 1940, with the 2pdr being sufficient for some time to come against the initial German tank types; however, having it in the desert would be very useful if combined with proper doctrine as compared to cavalry charges.
The point that stop-gap and emergency measures, particularly in regards to ASW, can be avoided with earlier rearmament is correct; the major factors in this calculation are German U-Boat construction numbers and much more significantly, the Fall of France. Without the use of French Atlantic ports, certain aspects of the U-Boat menace are reduced.
A salient point to keep in mind in discussions of rearmament is that we cannot allow our judgements to be clouded by rose coloured hindsight - simply beginning rearmament 1-2 years earlier in earnest does not solve production bottlenecks, faulty assumptions of the time, inefficient procurement or substantially change the operational thinking of what to do with the equipment acquired. As mentioned earlier, there is also the opportunity cost of moving to earlier war mobilization of the economy to take into account.
It does depend on when the decision is made, and how it is applied, rather than simply blanket rearmament. If the decision is made prior to 1934, then a lot more can be done regarding rebuilding the armaments industry after the collapse of the 20s:
- Palmers can possibly avoid closure
- Gunpits and armour plants can be ordered, allowing greater capacity when they come online in 2-3 years time
- Ship design can be altered
It would take some time to undo the decisions made in 22-24.
British defence expenditures 1930 to 1940 do indicate when a firm move was made, with defence expenditure and the proportion of GDP:
1930: 100 million (2.6%)
1931: 100 million (2.69%)
1932: 100 million (2.63%)
1933: 100 million (2.65%)
1934: 100 million (2.66%)
1935: 125 million (3.01%)
1936: 250 million (3.71%)
1937: 375 million (4.82%)
1938: 500 million (8.72%)
1939: 875 million (15.19%)
1940: 2500 million (37.78%)
(Figures based on material from Uk public spending, so may be off a little in terms of precision)
http://www.ibiblio.org/hyperwar/UN/UK/UK-Civil-WarProduction/UK-Civil-WarProduction-2.html
Salient materials can be found here to expand on some of these points
If things move into flow in 1934 as compared to 1936, then there will be some butterflies, both for good and ill. Whether there was the political will and support to justify such a move then is different.