Here's the solution I came up with ( for now ) to allow older devices to work and more recent devices to take full advantage of the GPU:
In the settings you now have a Toggle switch for enabling/disabling GPU:
All the devices in the following list will be initialised with the toggle switch off although you will still be able to override the initialisation and switch it on, you'll have to close the schematic and open again for the setting to take effect or somehow cause the canvases to reload:
iPad1,1 : iPad
iPad1,2 : iPad 3G
iPad2,1 : 2nd Gen iPad
iPad2,2 : 2nd Gen iPad GSM
iPad2,3 : 2nd Gen iPad CDMA
iPad2,4 : 2nd Gen iPad New Revision
iPad3,1 : 3rd Gen iPad
iPad3,2 : 3rd Gen iPad CDMA
iPad3,3 : 3rd Gen iPad GSM
iPad2,5 : iPad mini
iPad2,6 : iPad mini GSM+LTE
iPad2,7 : iPad mini CDMA+LTE
iPad3,4 : 4th Gen iPad
iPad3,5 : 4th Gen iPad GSM+LTE
iPad3,6 : 4th Gen iPad CDMA+LTE
iPad4,1 : iPad Air (WiFi)
iPad4,2 : iPad Air (GSM+CDMA)
iPad4,3 : 1st Gen iPad Air (China)
iPad4,4 : iPad mini Retina (WiFi)
iPad4,5 : iPad mini Retina (GSM+CDMA)
iPad4,6 : iPad mini Retina (China)
iPad4,7 : iPad mini 3 (WiFi)
iPad4,8 : iPad mini 3 (GSM+CDMA)
iPad4,9 : iPad Mini 3 (China)
iPad5,1 : iPad mini 4 (WiFi)
iPad5,2 : 4th Gen iPad mini (WiFi+Cellular)
iPad5,3 : iPad Air 2 (WiFi)
iPad5,4 : iPad Air 2 (Cellular)
iPad6,3 : iPad Pro (9.7 inch, WiFi)
iPad6,4 : iPad Pro (9.7 inch, WiFi+LTE)
iPad6,7 : iPad Pro (12.9 inch, WiFi)
iPad6,8 : iPad Pro (12.9 inch, WiFi+LTE)
iPad6,11 : iPad (2017)
iPad6,12 : iPad (2017)
iPad7,1 : iPad Pro 2nd Gen (WiFi)
iPad7,2 : iPad Pro 2nd Gen (WiFi+Cellular)
iPad7,3 : iPad Pro 10.5-inch
iPad7,4 : iPad Pro 10.5-inch
iPad7,5 : iPad 6th Gen (WiFi)
iPad7,6 : iPad 6th Gen (WiFi+Cellular)
iPad7,11 : iPad 7th Gen 10.2-inch (WiFi)
iPad7,12 : iPad 7th Gen 10.2-inch (WiFi+Cellular)
If this becomes an issue, I'll work on caching the preview canvases as images to improve performance of older devices.