So having done the 2 studies, there are a few points -
1. Centroliums and hyperiums definitely make a huge difference. The first test was with a digger at 46, and with the benefit of hindsight, 1000 clicks probably weren't enough considering how much centroliums and hyperiums can skew the overall silvers in 1000 clicks.
2. On average, the increase in silvers/click was around 44%
3.In order to compare the 2 results I've used ranking statistics. Basically I've ranked each square in both tests according to (a) silvers/click and (b) a multiple of silvers/click and xp/click - weighted equally. You could argue that the stats are slightly flawed, as I've omitted comparing xp/click only. The assumption behind this is that diggers (well, mine anyway!) don't only dig for XP. I've then combined the rankings for each test and compared the new combined ranking for both tests for each of the criteria. I've then run a Spearman test on the 2 sets of ranks, and got a correlation statistic of 0.87, which is pretty high.
So what does this all mean? Well - in short, digging in around the 2 casinos appears to yield both the highest silvers/click and combination of silvers and xp. Below is the table with final overall rankings per square using the results from both tests and both criteria.
From CC_________ Overall Rank
2S 3E 1S 1E______ 1
2S 3E 1S_________ 2
2S 3E____________ 3
2S 2E 1S_________ 4
4S_______________ 5
1S 2E____________ 6
2S 3E 2S_________ 7
2S 2E____________ 8
3S_______________ 9
2S 1E____________ 10
2S 3E 2S 1E______ 11
2S_______________ 12
4S 1W___________ 13
1S 1E____________ 14