I've decided I'm saving up for another mill (Chinese jobbie) to convert instead of the motor upgrade.
My X2 has come along well so far. Belt unit, R8 spindle upgrade, solid column squeezed 155mm travel on the Y axis, 420oz/in steppers, homemade 350w 20Litre coolant system (overkill and powerful!!!)
Gradually pushing up and gone up to 800mm/min with decent accuracy so far with a 6mm cutter but you can here the motor struggle a bit at times.

The new mill I'm looking at is bigger than the Grizzly G0704.
There's the Amadeal AMA30LV - R8 coming soon?
The Warco WM18
Only downside is these are gear driven
Then there's the TOOLCO WM32B which is belted.
All R8 out of stock atm and I'm impatient

All 3 say they have a good 220mm travel on the Y axis which appeals to me.Much bigger than a X3 for a close price tag around £1450.
I got slightly more Y travel than the X3 on my X2!