Would be fine I’m sure– I run Qu-Pad on an old iPad Mini and it is fine. The software is just a control surface really. Don’t think it has to work very hard.
I, or rather my kids, have an iPad2 and I have used QuPad on it for a while.
I *think* it’s updated to 1.9, but I’m not sure I’ve used it as a remote since firmware 1.9.
No issues that I know of – but I usually don’t need the second iPad connected (since I have the surface most of the time), and have an iPad mini (3) for general use.