Hi Steve,
You don't mention if you're using the reducer with the 72ED. This can make a difference.
Based strictly on the numbers, the 183MM would be more suited to your current setup & not bad with a larger scope like an 8" SCT or Newt, while the 1600MM would be the reverse, better for the larger scope but still quite useable with the 72ED.
Another option to consider is the 294MM. These have an "unlocked" bin 1x1 mode that the colour models don't. This gives you access to a pixel size very suitable for wider setups while the bin 2x2 is more suitable for a larger setup. Of course there are some drawbacks to this versatility you will need to consider - though it does still work well in 2x2 even with the smaller scopes.
The biggest 'drawback' for me is the file size of the unlocked 1x1, over 90MB each vs 22MB in 2x2. But depending on the size of the target I often use a ROI setup, greatly reducing the file sizes. I've never personally used either the 183MM or 1600MM, but I am very happy with the 294MM on both my 102mm refractor & 8" SCT.
And I do like the looks of the 533, was actually going to get an OSC version before the 294MM fell into my lap instead.
Cheers,
Mark