Minimum temperature for slow roasting almonds
I found these slides that may help. The information is a difficult to interpret, but the page with conclusions says that the optimal roast uses the lowest possible temperature for 20 to 30 minutes. This however is information for the food industry and it is clearly geared towards increasing shelf-life which you are probably not too concerned about.

If you look for the slide with the title 'Generation of flavor compounds during roasting', you will get another perspective. As I understand the graph, a roast at 200ºC (400ºF) for around 25 minutes gives maximum flavour.

This article, although about roasting walnuts, gives clearer information. It states that walnuts are typically roasted at 100-180ºC (212-356ºF) from 5 to 60 minutes. You could infer from this that roasting at 100ºC for an hour is as low and slow as you can go. The conclusion to this article is that the "best sensory properties" are exhibited after roasting at temperatures between 130-150ºC (266-300ºF) for 15 to 20 minutes.

I think that gives you at least four worthwhile experiments to try:


120ºC for 25 minutes (recommendation from the slides)
200ºC for 25 minutes (the time/temperature profile that appears to give maximum flavour)
100ºC for 60 minutes (the apparent limit of low/slow roasting walnuts)
140ºC for 17 minutes (the recommendation for roasting walnuts)


Update: I remembered a fact about the Maillard reaction that could point in another direction of experimentation. Although the reaction needs relatively high heat to get going, once browning has started, the reaction will continue at lower temperatures (as low as 60ºC is what I remember reading). So perhaps you could kick start the reaction by initially roasting at 150ºC (300ºF) or above and then dropping the temperature right down to around 75ºC (170ºF) as soon as browning starts.