gdgt

Logitech's Wireless Solar Keyboard K750 for Windows would work just as well if not better for your purposes. The only system-specific parts that make it a Mac or Windows keyboard are going to be the windows/apple button and a couple of other keys not frequently used. Generic bluetooth keyboards will also work just fine, especially the ones "designed for iPad" since they're typically just mass-market generic BT keyboards underneath the branding.

If it's powered by a Bluetooth connection, one size is probably going to fit all here. Windows bluetooth keyboards typically work with Macs and vice-versa, though Mac-specific keyboards tend to not translate well to Windows. Since you want a full form factor and ease of cross-compatibility I would spring for the Windows keyboard as it's more likely to work how you want it on both ends with minimal problems. Windows won't have problems with a keyboard designed for it, and your iPad should be able to adapt.

Full disclaimer: I've only had experience using Win BT keyboards on iMacs, but I would assume they share similar bluetooth drivers. Someone using a similar setup like what you're wanting may want to chime in to confirm/deny.

edit: Not finding anything saying that Logitech's K750 (for Windows as well as Mac) will not work on iPads, and the mac version of the 750 was marketed specifically to work for iPads and features Mac-specific keys and a full form factor. The K750 for Mac seems cheaper as it's the depreciated model under the K760 now, and I don't see why it wouldn't work on a PC if you're willing to dig up drivers for it. (Win drivers for the Windows version are available on Logitech's site.)

I'd look for the K750 for Mac or just go with the Windows version if I were you.