Big Agnes specs call for a 25" wide pad to be used with the Summit Park.
I have an Exped Synmat 7L that is 28" wide. Has anyone used that combination successfully?

You sure that is 28 inches wide? Exped lists it at 26.

that to me would seem stuffable..but I don't know your bag.

I have a Big Agnes Buffalo Park bag. The Park series bags all indicate "25" wide mattresses, because I think Big Agnes sells a 25 inch wide mattress. I have the Exped Synmat 7 Long & Wide which is 26" wide. It fits just fine. The key, of course, is not to inflate these mattresses where you can bounce coins off them, rather just to the point where you can push through the mattress to the ground with gentle hand pressure, or just enough to keep your hip bone from digging in to the ground when you're lying on your side. I suppose if you inflated it to max inflation, it might be a little more difficult to fit it into the sleeve.

I have a new Deer Park and my LW Synmats & Downmats fit fine. I put the pad in before I inflate it. It would fit either way however. I like my mats under-inflated so they feel like a pillow top.

Yeah, I'm not sure I've seen 28", I've seen lots of 25 and 26 and Nemo makes a 30. But as far as 25 vs 26 I have personally swapped out both and never had issues, 26" wide fit in bags made for 25" and of course 25" pads fit will in pags made for 26".

You guys are awesome as usual! I did indeed measure my pad uninflated. That would account for the extra inches. Thanks for the responses. I an going to order a new bag tomorrow.

Have you tried the new system?
How's it feel?