For the ASX 300 (or any ASX index) the market cap will be based...

For the ASX 300 (or any ASX index) the market cap will be based on the SP of A40.

Typically when you get large spreads between exchanges it's due to limited volume on one of the exchanges, or at least that's my experience. I expect reasonable volumes on both the ASX and SGX, so if we see large spreads I expect we'll see a fair amount of arbitrage trading.

If the ASX 300 rebalance were to occur now then A40 would be an addition. We will have to wait until March though before we'll find that out though.