My gf is about to get a new road bike and we are looking at a shoe / pedal combo that will work for both the bike and spin class.

I assume most spin classes use standard SPD? If so, I suppose an SPD pedal for the road bike combined with an MTB shoe w/ a stiff sole would be the best combo? I was looking at the XT M785 pedals as they have a full size platform + SPD cleat.

Recommendations?

It's the best combo for my wife, road and spin.

The spin class bikes do use SPD pedals (and platform on the other side for those without cleats). You'll need an SPD pedal on the road bike for the same shoes to be compatible with both bikes. I spin and use Shimano PD-A530 pedals on my bike (one side is a platform). I never use the platform side and will, at some point, replace the pedals on my road bike. That said, the A530's are decent pedals for the money.

Ya, the gf doesn't need platform ONLY side. I just figured the XT pedals I mentioned would be good as they have the SPD cleat surrounded by a larger platform to somewhat simulate a SPD-SL pedal in terms of surface area.

I've got the XT trail pedals on my mtb and my wife has just put some standard non-trail spd's on her road bike for an upcoming tour. I don't notice any contact between my mtb shoes and the trail cage/platform. They do however present a larger target if you pop a foot out in technical terrain and need to get it back on in a hurry. Mrs. Fred's sporting the standard double sided spd's with PI mtb shoes and seems to like them so far. A little bit of an adjustment was required with regard to picking the cleat up and engaging. But, nothing that 5 minutes on the trainer and two laps around the block couldn't solve.

On either pedal the entire contact area is the same (the metal to metal cleat interface).

Any of the road-like MTB shoes would be fine. There just as stiff as road shoes, but a bit heavier. I use A520's which are single-sided SPDs and have a bit of a platform surrounding the latch. They are very easy to clip into and reasonably light.

If you want a road shoe, specialized makes their entry level road shoes tapped for spd or spd-sl.

She would probably prefer an MTB shoe anyways so that she can get off and walk relatively comfortably.

Have her check out these Bontrager shoes. They are made for SPD, but have a smooth sole, great for spin or on the bike.

https://campusbicycle.com/product/bon...es-49289-1.htm