I just looked at SPY and DIA, and I suspect DIA is just as volatile.
SPY doesn't even seem to have options traded off it.
If you have over $25,000 in your account, then you will have access to 4:1 intraday margin.
But if you don't, the most you'll have is 2:1 margin. With DIA stock futures you'll get 5:1 margin, round the clock (without needing $25,000).
I'd suggest just add DIA to your trading page, and watch it in relation to SPY. You'll arrive at your own decision.